DICTIONARY OF
PHILOSOPHY AND PSYCHOLOGY

I and Me. Synonymous with subject-self and object-self. See SELF (also for foreign equivalents). (J.M.B.)

I (in logic). Symbol for the particular affirmative judgment: 'Some men are fools.' Cf. A (in logic). (J.M.B.)

Iamblicus (or Jamblicus). Lived in the 3rd and 4th century A.D. A Neo-Platonic philosopher, who was a disciple of Porphyry. Many of his writings are extant. See ALEXANDRIAN SCHOOL.

Iconolatry: see IMAGE-WORSHIP.

Id: see IDANT, and BIOPHORE.

Idant [no specific formation according to Weismann -- E.B.P.] (the same in other languages). The hypothetical unit resulting from the aggregation of biophores, determinants, and ids (all Weismann's terms).

Suggested by Weismann, 1891 (GermPlasm, Eng. trans., 1893). (C.LL.M.)

Idea [Gr. idea]: Ger. Idee, Vorstellung (presentation); Fr. idée; Ital. idea, rappresentazione. The reproduction, with a more or less adequate IMAGE (q.v.), of an object not actually present to the senses. (G.F.S.- J.M.B.)

The partial reproduction by the image is distinguished from actual perception by various alleged characteristics -- on which, however, authorities differ -- such as difference in degree of intensity and, perhaps, in kind of intensity, comparative absence of detail, comparative independence of bodily movement on the part of the subject, and comparative dependence on mental activity.

The earlier English usage is well exemplified by the following passage from Locke: 'I must at the entrance beg pardon for the frequent use of the word idea which he [the reader] will find in the following treatise; it being that term which I think best to stand for whatever is the object of the understanding when a man thinks. I have used it to express whatever is meant by phantasm, notion, species, or whatever it is which the mind can be employed about in thinking; and I could not avoid frequently using it' (Essay on Human Understanding, 1. vi. § 8). In this passage the term is applied to objects apprehended, and not to the subjective state or process of apprehending them. Further, objects as perceived by means of actual sensations are included under the term, as well as objects represented independently of actual sensations. In Hume the subjective process of apprehension is simply confused with the object as apprehended; but he makes a sharp distinction between perceptual experiences, which he calls impressions, and ideas, which are, according to him, always fainter reproductions of previous impressional experiences.

The German Vorstellung is not uncommonly used so as to cover both perception and idea in the narrower sense (cf. PRESENTATION). There has been a tendency to give the term 'idea' the same wide application in English. It is, for instance, so used in Titchener's Outline of Psychology. But the English tradition since Hume is against this usage, and there seems to be no good reason for adopting it. The definition either of percept or idea, or both, as a group of sensations or sensory elements, so-called 'centrally initiated sensations' (see SENSATION), implies a particular psychological theory. The definition we have given might be provisionally adopted by all psychologists.

Literature: LOCKE, loc. cit; HUME, Treatise of Human Nature, Bk. I. Pt. I. § 1; TITCHENER, Outline of Psychol., Pt. II. chap. vii. § 43, with which contrast Primer of Psychol., chap. vi. §§ 38-9; WARD, art. Psychology, Encyc. Brit. (9th ed.), 57 ff.; WUNDT, Physiol. Psychol., ii. 1 ff.; BALDWIN, Elements of Psychol., glossary. (G.F.S., J.M.B.)

Idea (in philosophy): see IDEALISM, and PLATONISM. Cf. also extensive citations in Eisler, Wörterb. d. philos. Begriffe, 'Idee.'

Idea-force. An idea considered as having a dynamic property or as being a force.

A rendering of the French Idée-force used by Fouillée (Psychol. des Idées-forces), who has developed the theory that mental development proceeds by the interplay of original idea-forces. (J.M.B.)

Ideal: Ger. (1) vorstellend ( = ideating), (2) ideal; Fr. idéal; Ital. ideale. (1) The adjective of IDEA (q.v.). See also IDEATION, for distinction from ideational.

(2) That which we suppose would be completely satisfying, if we were able to attain it, is called the ideal of its kind: the moral ideal is the morally satisfying; the ideal self, the self which would have no lack to itself; the aesthetic ideal, that which satisfies the demand for beauty; the ideal gun, one that satisfies the requirements of accurate shooting.

The mode of consciousness involved in 'setting-up,' 'entertaining,' or 'having' an ideal is complex and obscure. Many writers consider the ideal a conception, but one rarely, if ever, realized in knowledge, life, &c. But it seems to be a part of this state of consciousness that the demand goes out beyond the actual conception; it never stops with the relatively satisfying, but aims always at what is still more satisfying.

Other writers accordingly find the ideal to be not an actual thought or conception, but a mixed conative-affective mode, which is a function of the actual thought: a mode which essentially anticipates further thought, and so demands something that can never be actually apprehended by thought. This meets the great difficulty that no one can state his ideal, in any department of knowledge. The case is not different in those instances in which the ideal seems to be fulfilled, as when we say that the circle fulfils the ideal of roundness; for there the term ideal has the meaning merely of adequate definition, and the peculiar mode of consciousness in question is not present at all.

The conative element in the psychosis is so strong that the term is mainly significant in spheres demanding achievement and practical adjustment; in philosophical construction art, and conduct. The term is used in ethics (see IDEAL, moral, and END) for the theoretical determination of the highest end. But great confusion has arisen from the failure to distinguish what such an ideal would consist in, and the individual's state of mind of which his ideal is a function. It is quite possible that the nearest approximation to the ideal of the ethical life is realized when the individual's end is subserving an ideal of a very different character.

But the intellectual characteristics of the ideal are embodied in the constructions actually made, and progress toward the ideal is made only by a series of such embodiments. It is this which differentiates and marks off an ideal. In this sense the ideal is thought or conceived. It is a sort of imminent end which dominates the scheme of development; although for this very reason consciousness cannot anticipate its own outcome, nor grasp the ideal itself in a single act of thought. Cf. INTENT.

Literature: general works on psychology and ethics. (J.M.B., G.F.S.)

Ideal (in aesthetics). (1) Consisting in ideas, having meaning or significance, as contrasted with the formal or sensuous element in a work of art; e.g. the ideal content of a picture, of music, &c. (2) A self-existing, changeless archetype, of which all finite forms or human images of beauty are imperfect copies, i.e. Plato's idea of beauty (see BEAUTY, I). 'The true and absolute ideal is God' (Cousin). (3) The embodiment in an individual (real or imaged) of what is valued aesthetically by an individual, a race, &c.; e.g. 'Apollo was the Greek ideal of manly beauty.' This may take three distinct forms: (a) what belongs especially to the TYPE (q.v.) may be emphasized to the neglect of the distinctively characteristic (so Winckelmann's conception of the Greek ideal); (b) what is distinctively characteristic of the individual may be intensified (rare); (c) the representation may be modified freely under the influence of more subjective considerations, viz. the artist's own personal selection of the point of view, or of the aspects of the subject or scene which appeal to his aesthetic feeling (the more usual popular conception of the term). (4) Actually embodying some concept or value, as 'He made an ideal Hamlet' (this is similar to (3), but is wider as involving the notion of corresponding to a concept as well as a value, and is thus akin to the mathematical and physical use of the term; e.g. an ideal solid is one that is perfectly rigid). (5) Existing merely in idea, opposed to real. This use seems to be derived from both (1) and (3 c). (6) Arising from an idea and having the unity characteristic of an idea, in the phrase 'ideal motion' used by Gurney to describe the process of perceiving musical form (Power of Sound, chap. viii).

For the discussion as to the nature of the ideal see IDEAL, BEAUTY, IV, and ART, III, and cf. CHARACTERISTIC, and EXPRESSION. For the process of forming ideals, see IMAGINATION, and IDEALIZATION.

Literature: see the general histories of aesthetics, given under ART, and BEAUTY; for the present usage, the works under AESTHETICS, and especially those under IDEALIZATION and REALISM. See also BIBLIOG. D, a, d. (J.H.T.)

Ideal (moral). (1) That which we suppose would satisfy our moral nature if we were able to attain it. Cf. IDEAL (2).

As contrasted with moral END (q.v.), the ideal is a state of attainment reached by the pursuit of the end. It is, therefore, rather an INTENT (q.v.) than an end. It is important that this distinction should be made, since the question of the ideal is often made the same as that of the end; that is, it is sought to determine the ideal in terms of the individual's end. (J.M.B.)

(2) The conception by reference to which man's conduct should be regulated, or to which his character should be assimilated.

Wherever independent ethical reflection has arisen, a rule or standard has been sought for the discrimination of right from wrong; and this rule or standard is either itself the ideal for man's conduct and character or results from that ideal. The term arose from the Platonic use of 'idea' for the true nature or essence of a thing. The moral ideal is thus the essence of goodness; and, in modern usage, the employment of the term 'ideal' instead of 'idea' indicates that this essential goodness is not actually realized, but in need of realization.

Different conceptions of the ideal of man fix the differences of ethical schools. Thus the various hedonist and utilitarian schools maintain that the realization of pleasure, in some form or other, is the ideal; while other schools hold it to be the perfection of the individual and social nature or the performance of the moral rules laid down by each man's conscience. Cf. ETHICAL THEORIES. (W.R.S.)

Ideal Realism: see REAL IDEALISM.

Idealism [Gr. idea, idea]: Ger. Idealismus; Fr. idéalisme; Ital. idealismo. (1) In metaphysics: any theory which maintains the universe to be throughout the work or the embodiment of reason or mind.

(2) In epistemology: the view which holds in opposition to REALISM (q.v.), that the reality of the external world is its perceptibility.

(1) In this reference, the so-called absolute idealism of Hegel, with its thesis of the convertibility of the real and the rational, is a consistent and ultimate formulation of the position. But any theory which seeks the explanation, or ultimate raison d'être, of the cosmic evolution in the realization of reason, self-consciousness, or spirit, may fairly claim to be included under this designation. For the end in such a system is not only the result, but, as the determining prius of the whole process, is also the true world-building power.

The diametrical opposite of idealism in this sense is materialism or, as it has sometimes been styled, NATURALISM (q.v., 2). According to this view, consistently formulated, the universe is simply a brute fact, or collocation of brute facts, under the sway of mechanical law, 'Verily, not by design,' as Lucretius puts it, 'did the first beginnings of things station themselves each in its right place guided by keen intelligence, but because, many in number and shifting about in many ways throughout the universe, they are driven and tormented by blows during infinite time past; after trying motions and unions of every kind, at length they fall into arrangements such as those out of which this our sum of things has been formed, and by which it is preserved through many great years when once it has been thrown into the appropriate motions' (De Rerum Natura, i. 1020). In other words, the apparently rational system of the present cosmos is represented as a happy accident, resulting from one of the infinite casts of nature's dice. This system might be fitly called the Democritic, as the idealistic might be styled the Platonico-Aristotelian. The principle of the one is anagkh, blind necessity or fate; the principle of the other is purposive reason.

The first historical system to which the name of idealism is applied by common consent is that of Plato. In Plato's system reality does not belong to the ever-changing world of sense; true being is found in the incorporeal essences or ideas, which communicate to phenomena whatever permanent existence and knowability they possess. These pure forms exist in a supersensuous world by themselves, and their relation to the world of phenomena is indicated by Plato only by the help of metaphors. The ideal world of Plato is thus not so much a world of spiritual or self-conscious existence as of abstract reason -- a system of abstract rational conceptions, regarded as substances and powers. It must be allowed, however, that in his account of the Idea of the Good, the highest and, in some ways, the all-embracing concept, he formulates in his own way the same idea of an absolute self-realizing End which is the central thought of the Aristotelian system. But idealism, when it fails to demonstrate its thesis of the omnipotence and omnipresence of mind as the all-sufficient explanation of the facts of existence, relapses into dualism; and this relapse is represented in Plato by the necessity of invoking, besides the world of true being, a secondary or accessory cause to mh on, which he elsewhere designates anagkh, and which has to a certain extent the power of hindering the perfect realization of the ideas, and thus of thwarting the purposeful working of the Good. Aristotle, by his profound conception of development, goes far to overcome the dualism involved in the transcendent form of Plato's statement, but he also fails to eliminate the non-rational element involved in phenomenal existence. The Aristotelian prwth nlh, or wholly unformed matter, is defined as mere possibility which is not actual. Yet, says Windelband, it is not merely that which is not-being, but the accessory cause, which evinces itself as such through real effects (to ou ouk aneu -- sine qua non). Its reality is shown in the fact that the forms do not completely realize themselves in individual things, and that from it side-workings (parafuaV) proceed, which are without connection with the purposively active form, or are even in contradiction to it. From matter arises that which is conceptually indeterminate (sumbebhkoV) or the accidental (autsmaton) -- the lawless and purposeless in nature. Hence the Aristotelian doctrine distinguishes, in its explanation of nature, as did Plato in the Philebus, between final causes (to ou eneka) and mechanical causes (to ex anagkhV): the former are the forms which realize themselves in matter; the latter reside in matter, out of which proceed side-workings and counter-workings. Thus the cosmic processes are regarded by Aristotle ultimately under the analogy of the plastic artist, who finds in the hard material a limit to the realization of his formative thought. This material is, indeed, so far related to the idea that the idea can present itself in it, at least in general, and yet it is in so far a foreign, and thus an independent, element, that it in part opposes itself as a retarding principle to the realizing of the forms. Ancient philosophy did not overstep this dualism between the purposive activity of the form, on the one hand, and the resistance of matter on the other.

In modern philosophy the term idealism, in this metaphysical significance, has been mostly used in connection with the speculative systems developed by Fichte, Schelling, and Hegel, out of the critical philosophy of Kant. Kant speaks of his own philosophy as 'transcendental idealism,' but, as so applied, the term is used in an epistemological reference which will presently be explained. The Kantian scheme might, indeed, be described as idealism in the metaphysical sense, inasmuch as it regards the kingdom of ends -- the ethical commonwealth of self-legislating spirits -- as the noumenal world or ultimate reality, of which the world of sense is the phenomenalization. 'Nature,' Kant says, 'assumes a unity which does not otherwise belong to it, and becomes a realm or system, only when viewed in relation to rational beings as its ends.' (Werke, iv. 286, ed. Hartenstein, 1868). But the term is not so used by Kant himself. Fichte, however, accepting from Kant the primacy of the practical reason, claims the name idealism as the distinctive appellation of his own system, and draws an elaborate series of distinctions between idealism and the opposite point of view, which he calls dogmatism. The ego, not as a fact or a thing but as a self-realizing activity (Thathandlung), constitutes the principle of his own theory; every doctrine, on the contrary, is dogmatic which starts with the existence of things and, taking the ego as a thing among things, explains it in the last instance as their product (see the 'First Introduction to the Wissenschaftslehre,' Werke, i. 419 f.; also i. 119 f.).

It used to be customary to describe Fichte's system as 'subjective' idealism in contrast to the 'objective' idealism of Schelling and the 'absolute' idealism of Hegel. The justification for such a usage was found in his method of starting with the ego, and regarding the non-ego simply as the antithesis or opposite of the ego -- the obstacle (self-imposed, no doubt, and necessary, but still an obstacle) to the realization and complete self-expression of the intelligent and ethical self. But the usage is misleading, in so far as the ego with which Fichte starts is not the individual but the absolute ego. Moreover, the term subjective idealism has come to be used exclusively in an epistemological reference. Fichte himself describes his idealism as 'practical.' 'Our idealism is not dogmatic but practical, that is, it determines not what is but what ought to be' (Werke, i. 156). Nature, according to him, is simply the material for the realization of duty, and duty is an eternal sollen or thou shalt, inspired by 'the idea of our absolute existence.' 'The ego demands that it shall embrace all reality and fill infinity. At the bottom of this demand there lies necessarily the idea of the absolutely posited infinite ego' (i. 277). But this 'idea of the ego' exists only as an ideal. The completion of the task would mean that the ego had subdued all things to itself, and was able to view them as determinations of its own existence, but the extinction of opposition would signify the cessation of the strife on which morality and consciousness depend. Hence the ideal is in its very nature unrealizable. It was this 'practical' character of his idealism which made Fichte an ethical reformer, and inspired his famous Addresses to the German Nation. But from a metaphysical point of view the theory was attacked by Schelling and Hegel as an imperfect statement of the idealistic position, inasmuch as it presents the idea as a mere sollen -- an ought-to-be, which never completely is. Schelling's 'objective' idealism regards 'nature as visible intelligence, and intelligence as invisible nature.' In other words, nature, apart from the moral activity of conscious beings, is already a system of ideal forms, and is therefore to be regarded not merely as non-ego, or an obstacle to be overcome, but as itself the expression of the same reason which comes to self-consciousness in man. Or, according to the somewhat later version of Schelling's theory, known as the IDENTITY PHILOSOPHY (q.v.), subject and object are parallel expressions of absolute reason, which, in itself, 'coincides precisely with the indifference-point of subjective and objective.' Hegel's 'absolute' idealism regards both nature and history as applied logic. Nature is merely 'the other' of reason -- a petrified intelligence, as he says in the Schellingian manner -- and in history we have the process of absolute spirit, the necessary stages on its way to complete self-realization. The universe is claimed, therefore, as rational through and through and to the smallest detail; 'the real is rational and the rational is real.' Or, as he says again in the Philosophy of Right, 'the task of philosophy is to understand the "what is," for "what is" is reason.' In markeo antithesis to Fichte, he disclaims for philosophy the rôle of the reformer; the idea is in fact eternally realized. Hegel even goes occasionally so far as to represent progress as, from this, the speculative point of view, an illusion. 'The consummation of the infinite end consists merely in removing the illusion which makes it seem still unaccomplished. This illusion it is under which we live, and it alone supplies the actualizing force on which our interest in the world depends. In the course of its process, the idea makes itself that illusion by setting up an antithesis to confront itself, and its action consists in getting rid of the illusion which it has created' (Wallace, Logic of Hegel, 304). Even Hegel, however, seems, in those passages in which he speaks of 'the range of the contingent' in nature and history, to surrender the claim to demonstrate the utter rationality of existence. 'Who but a Hegelian philosopher,' says Professor James trenchantly, 'ever pretended that reason in action was per se a sufficient explanation of the political changes in Europe?' (Princ. of Psychol., i. 553). Whether, therefore, we look at Aristotle or at Hegel, it would seem as if it were impossible for the finite mind to carry through in detail a demonstration of the rationality of existence, and as if faith, accordingly, must unite with insight in the idealistic creed.

(2) Quite a different sense of the term 'idealism' emerges in connection with epistemology or theory of knowledge. In this reference, which belongs entirely to modern philosophy, idealism, more precisely defined as 'subjective idealism,' is opposed to realism. The realist is one who considers that in sense-perception we have assurance of the presence of a reality, distinct from the modifications of the perceiving mind, and existing independently of our perceptions. The idealist, on the other hand, asserts that the reality of the external world is its perceptibility; as Berkeley, the founder of modern idealism, expressed it, the esse of things is percipi. Mill's so-called 'psychological' theory of the belief in an external world, which resolves its reality into actual sensations and permanent possibilities of sensation, is probably the most typical recent form of the theory. Kant's definition of idealism in the Prolegomena, framed with Berkeley in view, applies equally to the more modern version: 'Idealism consists in the assertion that there are no other than thinking beings, that the other things which we believe ourselves to perceive are only ideas in thinking beings -- ideas in fact to which there is no correspondent object outside of or beyond the thinking beings.' Idealism, in this sense, may be said to be the outcome of the belief that the mind is primarily limited in knowledge to a perception of its own subjective states, or, as Locke puts it, that 'the mind in all its thoughts and reasonings hath no other immediate object but its own ideas which it alone does or can contemplate' (Essay, IV. i. 1). 'It is evident,' he says elsewhere, 'the mind knows not things immediately, but only by the intervention of the ideas it has of them.' This may be said to be the common presuppositions of modern philosophy from Descartes to Hume. It is common to Descartes and Locke, who believe in the independent existence of the external world, and to Berkeley and Hume who deny any such inference. It is inherent in Leibnitz's conception of 'windowless' monads, and in Spinoza's view of the attribute of thought as self-contained. Reid calls it 'the ideal theory' or 'the theory of ideas,' and traces to this root the scepticism of Hume, to which he opposes his own doctrine of natural realism or natural dualism. Kant's Refutation of Idealism is directed against the same presupposition -- namely, that the only indubitable certainty is the certainty of our own internal states, and that this certainty constitutes (as Descartes makes it do) the starting-point of knowledge. From this point of view, the term idealism acquires in the hands of Kant and of Hamilton (elaborating the doctrine of Reid with Kantian additions) a wider application. Thus the doctrine of Descartes, who is, of course, not an idealist in the sense of denying the independent existence of the external world, is called by Kant 'problematical idealism,' because, by treating the res extensa as a matter of inference and belief, it places its reality on a lower level of certainty than that of our internal states. Hamilton applies the term 'cosmothetic idealism' (or 'hypothetical dualism'), in the same reference, and with precisely the same implication, to 'the great majority of modern philosophers' (Lects. on Met., i. 295). As distinguished from such a position, idealism in the stricter sense -- the subjective idealism of Berkeley -- is called by Kant 'dogmatic idealism.' He also uses the term 'material idealism' to include both varieties -- the problematic and the dogmatic -- in contra-distinction to his own theory of 'formal,' 'critical,' or 'transcendental' idealism.

Consistent subjective idealism would seem to involve not only a denial of the reality of other persons (solipsism), but a sensationalistic scepticism like that of Hume, which resolves the thinker himself into a series of 'perceptions,' regarded as facts pure and simple, without any cognitive value whatever. Hence it is explicable how Spencer, in his polemic against idealism (Princ. of Psychol., Pt. VII), persistently links idealism with scepticism -- a conjunction which aptly illustrates the wide divergence between the epistemological sense of the term idealism, and the metaphysical usage which was discussed in the first part of this article.

The term 'transcendental idealism,' as applied by Kant to his own theory, refers only to the formal elements of experience -- space and time and the categories. These constitute, 'the pure schema of possible experience,' but do not apply to things in themselves; in Kant's language, they are 'transcendentally ideal,' that is to say, of merely subjective validity. In a general regard, Kant's theory of knowledge is to be classed as realistic or dualistic, inasmuch as, according to his own statement, it had never entered into his head to doubt the existence of things in themselves. Cf. PHILOSOPHY, EPISTEMOLOGY, METAPHYSICS, REALISM, KANT'S TERMINOLOGY, and HEGEL'S TERMINOLOGY.

Literature: PAULSEN, Introd. to Philos., ii. chap. i; KÜLPE, Introd. to Philos., §§ 5, 26; EUCKEN, Grundbegriffe d. Gegenwart, 244 f. (A.S.P.P.)

Idealism (in aesthetics): (1) An aesthetic standpoint or theory which emphasizes the ideal or content element in beauty, opposed to FORMALISM (q.v.), IMPRESSIONISM (q.v.), and SENSUALISM (q.v.). It may be either (a) abstract, ideas being transcendental copies or ideals (Plato, Schelling); or (b) concrete, the idea being an immanent principle (v. Hartmann, Aesthetik, i. 27). See under BEAUTY, IV. (J.H.T.- K.G.)

(2) As opposed to realism, a theory of art which lays emphasis on the artist's idealization or modification of his material and construction of his work, according to subjective values, as contrasted with an objective reproduction. This in common usage often implies a less concrete and individualistic representation. Cf. IDEAL (in aesthetics), (3, a and c).

Literature: see under FORMALISM, IMPRESSIONISM, and REALISM. (J.H.T.)

Ideality: Ger. Idealität; Fr. idéalité; Ital. idealità. Ideal quality; used (in aesthetics) especially with reference to meanings (1), (3, a and c) of IDEAL (in aesthetics, q.v.). (J.H.T.)

Idealization (aesthetic): Ger. Idealisierung; Fr. idéalisation; Ital. (not in use). (1) The apprehension of truths or facts as fit for construction in an ideal.

The limits of idealization would seem to be, (a) the partial embodiment of the particular sort of ideal already in the truths or facts which are idealized. This partial embodiment prescribes the direction or character of the idealization. (b) The carrying over of the particular value -- aesthetic, moral, &c. -- attaching to the truths idealized, to the ideal, with exclusion of what is opposed or inharmonious. The ideal interpretation, it is felt, is thus and thus on the basis of these items of knowledge; that is, it is the sort of ideal which these particulars suggest. (J.M.B.)

(2) The process of giving meaning as under IDEAL (in aesthetics (1), q.v.), or of forming an ideal in either of the senses given under IDEAL (in aesthetics (3), q.v.).

Literature: VOLKELT, Aesth. Zeitfragen (1895), chaps. ii-iv; FECHNER, Vorschule d. Aesth. (1876); SANTAYANA, Sense of Beauty (1896), 112 ff.; SIEBECK, Das Wesen d. aesth. Anschauung (1875); SÉAILLES, Essai sur le Génie dans l'Art (1897); HODGSON, Met. of Experience (1898), iii. 384 ff.; SULLY, Human Mind, i. 377 ff.; BALDWIN, Feeling and Will, 198 ff.; DEWEY, Psychology, chap. vii; ALLEN, Physiol. Aesth. (1877), chap. ix. (J.H.T.)

Ideas of the Reason: see KANTIAN TERMINOLOGY, 10-21.

Ideation: Ger. vorstellende Thätigkeit; Fr. idéation; Ital. attività rappresentatrice, ideazione. Mental process which takes the form of a succession of ideas. Suggested and explained by J. S. Mill, Logic, ii. 216.

The adjective form 'ideational,' as applied to such a process, is more exact than is ideal. (G.F.S.- J.M.B.)

Ideatum [Lat.]. The OBJECT (q.v.) of cognition. (J.M.B.)

Identical Points: Ger. identische Punkte; Fr. points identiques des rétines; Ital. punti identici. Retinal points which, when the eyes are in the primary position, occupy coincident positions in relation to the centre of the retina, and correspond to coincident image points of an infinitely distant object.

The identical points are for anatomy what the corresponding or CONGRUENT POINTS (q.v.) are for physiology. Their discussion in modern times dates from J. Müller (Helmholtz, Physiol. Optik, 2nd ed., 914; Wundt, Physiol, Psychol., 4th ed., ii. 222). A theory of visual space perception, long current (more especially in physiology), and represented in modified form by Brücke and Volkmann, was based upon them.

Literature: HELMHOLTZ, Physiol. Optik (2nd ed.), 844, 913; WUNDT, Physiol. Psychol. (4th ed)., ii. 173; HERING, in Hermann's Handb. d. Physiol., III. i. 354, and Beitr. z. Physiol., i. (1861) 20 ff., ii. (1862) 81 ff.; AUBERT, Physiol. Optik, 605; BRÜCKE, Müller's Arch. (1841), 459; VOLKMANN, Arch. f. Ophthal., V. ii. (1859) 86; and art; Sehen in Wagner's Handwörterb. d. Physiol., III. i. 316 f., 340 f. (E.B.T.)

Identity (apprehension of individual) [Lat. idem, the same]: Ger. (Erkenntnis der) individuellen Identität; Fr. (perception de l') identité individuelle; Ital. (percezione dell') identità individuale. (1) Recognition of a thing as different from all other things, and including in its unity all its inner changes and other diversities. Such a thing is said to remain the same or to have sameness.

(2) Sometimes used for PERSONAL IDENTITY (q.v.).

The recognition seems in general to depend on unity, continuity, and exclusiveness of interest. Thus a thing may be regarded either as identical or not identical, according to the varying subjective point of view. See RECOGNITION, and cf. INDIVIDUAL. (G.F.S.- J.M.B.)

For instance, various qualities and modes of behaviour presented through the separate senses of touch, sight, hearing, &c., combine for our apprehension in the unity of a single thing, because the presentations of these different sense co-operate in processes having unity of practical interest. The nucleus or unifying centre is the experience of resistance connected with the actual manipulation of things at close quarters, by which we change or endeavour to change their position and shape by our effort. Practical efficiency in the attainment of the ends of animal life is predominantly constituted by movements which either take the form of effort put forth against resistance or prepare the way for such effort. But the sensations of sight, touch, sound, smell, and taste, proceeding from the same material thing, co-operate in the most intimate way in leading up to and guiding movements of manipulation. It is primarily through this unity and continuity of practical interest that they become united for consciousness as constituting one and the same external object. Similarly, a series of changes in time is included in the unity of a single thing if the changes do not disturb, or if they actually subserve, the development of the distinctive interest which is aroused. The cat chasing a bird apprehends the bird as one and the same individual in all its changes of position and posture. Such changes merely serve to determine successive phases and stages in the development of its own activity. Similarly, the bird when killed is identified with the bird alive. The death of the bird is only a stage in the process which finds its end-state when the bird is eaten.

Mere unity and continuity of a distinctive interest are not in themselves sufficient to constitute the cognition of individual identity. As Royce has recently pointed out, the interest must be 'exclusive.' A child 'has a play-thing, say a lead soldier. He loves it. He breaks it. Now offer him . . . another play-thing -- another lead soldier, as nearly as possible like the one just broken. Were the broken one not as such before the child's mind, the new one might prove in all respects satisfactory. But now, will the child . . . be very likely to accept the new soldier as a compensation for the broken one? No! . . . Now at this moment, I say, when the child rejects the other object -- the other case that pretends to be an apt appeal to his exclusive love for the broken toy -- at this very moment he consciously individuates the toy.' Royce seems to be clearly right in insisting on the necessity of exclusive interest. But the present writer cannot agree with him in demanding that the exclusiveness shall assume the highly developed form which attaches to it in the example of the broken toy. Before the toy was broken, the child must already have taken an exclusive interest in it. The accident and the proffered substitution only brings home to him the fact that his interest in it is exclusive. But to have an exclusive interest is one thing; to distinctly recognize that the interest is exclusive is another. The exclusive interest and the correlated apprehension of individual identity are the pre-condition of the passionate rejection of a substitute. Royce's statement therefore puts the cart before the horse. His view breaks down in such simple cases as that of the cat chasing the bird. The bird is throughout the same individual for the cat which is pursuing it. But it would make no difference to the cat if another bird exactly like it were substituted. The exclusive interest arises from the fact that no other bird is substituted. No others may be present; and if they are, the cat can only chase one of them at a time, because it has itself only one body, and can therefore only execute one set of movements at once. Exclusiveness of this kind is the necessary presupposition of exclusiveness in Royce's sense. Unless the child is, to begin with, able to recognize his tin soldier as just this individual tin soldier numerically distinct from others, he cannot learn to love it in an exclusive manner. The exclusive love is due to growth of memories, associations, and connected sentiments, which attach to this individual object as such, and not to others. But this would be impossible unless the object were, to begin with, apprehended in its individual distinctness. The growth of these memories, associations, and sentiments constitutes a second and more advanced stage in the process of individuation. A third stage arises with the loss of the loved object, and the felt impossibility of compensating for this loss by substituting any other.

Literature: WARD, art. Psychology, Encyc. Brit. (9th ed.), 80 f.; ROYCE, The Conception of God, v (Suppl. Essay), Part III. Also citation under INDIVIDUAL. (G.F.S.)

Identity (apprehension of material): Ger. (Erkenntnis der) inhaltlichen Identität; Fr. (appréhension de l') identité matérielle; Ital. (percezione dell') identità materiale, or identificazione. RECOGNITION (q.v.) based on complete apparent likeness. Cf. Ward, art. Psychology, in Encyc. Brit. (9th ed.), 80 f. (G.F.S., J.M.B.)

Material identity is the limiting case of RESEMBLANCE (q.v.). When I say that the green of this leaf is identical with the green of that, I mean that the colours are exactly alike, and mean to assert material identity. When I say that I have the same body which belonged to me as a baby, I mean to assert individual identity (see the preceding topic).

Identity (in metaphysics). The principle of absolute equality with itself of what is real; the principle that the law of IDENTITY (in logic, q.v.) is also a principle of reality.

Identity is both an assumption of thinking and a postulate concerning the nature of reality. The hypothesis of 'bare identity,' or 'distinctionless being,' is opposed by that of 'identity in difference,' according to which identity and difference are correlative and mutually dependent conceptions, identity being relative to difference and difference presupposing identity. This is undoubtedly sound as a criticism of these categories of thought as such; but it is mere tautology in relation to concrete matters of fact or of science, or, more broadly, to the process of knowledge as concretely determined. For here it is always one side or the other -- identity or difference -- which subserves the interest of the thought or action, and the determination of an identity in difference says nothing as to the extent or form of either. For example, to say that heredity is a law of identity in difference, leaves the extent of likeness and variation quite untouched; so also to say (see Bosanquet, Mind, April, 1899) that imitation and invention are both covered by the formula 'identity in difference.' Difference as a conception is fruitful as lending itself to one sort of method and to one sort of data, identity to another sort of each; just as in the genetic development of consciousness, the discernment of difference and distinction is a later and more complex act than that of the vague generalization which proceeds upon resemblances. So while they are logically correlative, and existence is always both, yet to the thought which makes use of these categories identity is an abstraction from differences and difference from identities.

Identity considered as principle of permanence and changelessness in being, contrasted with the flux of the phenomenal, dates back to the Eleatics. See PRE-SOCRATIC PHILOSOPHY. Cf. also CHANGE, and, for the place of identity in the Hegelian dialectic, HEGEL'S TERMINOLOGY, III, IV.

Literature: works of general metaphysics, as in BIBLIOG. B, I, c; also see the indications under the other topics IDENTITY. (J.M.B., G.F.S.)

Identity (logical). The principle that a logical term is always equal to itself (A = A) and to nothing else. Cf. CONTRADICTION, and see LAWS OF THOUGHT.

This principle states a logical demand or ideal of thinking rather than a psychological fact. The identity which formal logic supposes is an abstract or symbolic representation requiring a sameness in the content of the term which is never fully realized. The substitution of A for A is valid only without the psychological context in which A is a matter of experience. In dealing with universals and with definitions the principle of identity is both logically and psychologically valid, since, in the former case, the limit of material modification has been reached, or is formally assumed, and, in the latter case, material modification is expressly excluded. The hypostatizing of identity as a metaphysical principle assumes the metaphysical validity of this logical category. Cf. the other topics IDENTITY. (J.M.B.)

Identity (personal): see PERSONAL IDENTITY.

Identity in Difference: see IDENTITY (in metaphysics).

Identity-philosophy: Ger. Identitätsphilosophie; Fr. philosophie de l'identité; Ital. filosofia dell' identità. (1) The theory which, metaphysically, reduces mind and matter, the ideal and the real, thought and being, to unity in the absolute (cf. IDEALISM, MONISM, and PANTHEISM); or, phenomenally, looks upon the physical and the psychical series as correlative 'sides' or 'aspects' of one and the same process. Cf. DOUBLE ASPECT THEORY, and PARALLELISM (psychophysical).

(2) In particular, the system propounded by Schelling in the second and most significant stage of his philosophical development (Falckenberg, Hist. of Mod. Philos., 447, 456-61), in which, through a combination of Spinozistic and Fichtean principles, he reaches the conclusion that object and subject, real and ideal, nature and spirit, are one in the absolute, which is the identity or indifference of both (Ueberweg, Hist. of Philos., ii. 213).

Fichte, in his subjective or transcendental idealism, had subordinated the objective or real element in the world to the subjective or ideal. Schelling adds the philosophy of nature to the science of knowledge with co-ordinate rank, and then interprets nature and spirit as alike proceeding from a neutral ground which is above them both. This identity divides by polar opposition into the negative or real pole (nature, object) and the positive or ideal pole (spirit, subject); but in itself it is the identical ground or indifference of the two. This system of identity was set forth in a series of writings which appeared in rapid succession in the first decade of the 19th century (Darstellung meines Syst. d. Philos., 1801. Bruno, oder ü. d. göttliche u. natürliche Prinzip d. Dinge, 1803; Vorlesungen ü. die Methode des akademischen Studiums, 1803).

Of contemporaries and followers of Schelling, Wagner, Friedrich Krause, Schleiermacher, and Hegel may be mentioned among those who felt the influence of the doctrine. In his absolute idealism, Hegel developed a monism of logical reason which combined the Fichtean emphasis of spirit with Schelling's insistence upon the philosophy of nature; but he energetically repudiated the conception of the absolute as an indeterminate neutrum, as well as the intellectual intuition by which Schelling claimed to attain a knowledge of the identical ground, together with his (lack of) derivation of nature and spirit therefrom (Hegel, Phänomenologie des Geistes, Vorrede; Schwegler, Hist. of Philos. x1iv; Falckenberg, op. cit., xii. 1). Cf. Simone Corleo, La Filosofia dell' Identità (1879-80). (A.C.A.Jr.)

Ideogenetic Theory (of judgment). Brentano's view of the original character of JUDGMENT (q.v., also BELIEF), known by his school (Hillebrand, Meinong, Höfler) as the ideogenetische Urtheilstheorie. (J.M.B.)

Ideogram (or -graph) [Gr. idea, idea, + graqein, to write]: Ger. Ideogramm; Fr. idéogramme; Ital. ideogramma. A written sign or symbol, not a name, which conveys its meaning by its own form, being often a pictorial representation (a pictograph) of the object symbolized.

The ideograph characterizes an important stage in the primitive evolution of writing. It is contrasted with a phonogram, which is a written representative of a thing or idea through the vocalized name for the thing or idea; occasionally, as in imitative sounds, onomatopoesis, it represents the sound itself. Our own language and those from which it is derived are of course phonographic. As examples of ideographic records may be cited the pictographs of North American Indians, and (in part) Mexican writings and Egyptian hieroglyphics. Ideographic survivals in current usage are the Roman numerals, I, II, III; zodiacal, astronomical, and certain zoological signs, e.g. 4, denoting Jupiter -- an arm grasping a thunderbolt. Ideographic elements in the letters of the alphabet are abundant. Such characters, however, pass quickly into conventional stages and lose much of their original form.

Literature: works on the origin of writing; HOFFMAN, The Beginnings of Writing (1895), 209; BRINTON, Essays of an Americanist (1890). (J.J.)

Ideogram (in psychology). The curve or tracing secured with a recording apparatus (Ideograph) arranged to exhibit variations of muscular movement occasioned by changes in thought. See Morselli, Semej. mal. ment. ii (1895), for its use in pathology. (J.M.B.)

Ideology [Gr. idea, idea, + logoV, discourse]: Ger. Ideologie; Fr. idéologie; Ital. ideologia. The continuation and development, in the period of the Revolution and the immediately succeeding period, By Destutt de Tracy (the author of the term), Cabanis, and others, of the French sensationalism of the 18th century (Condillac). The ideologues made the analysis of ideas, and, in particular, the investigation of their origin, the fundamental philosophical discipline, which at the same time was expected to furnish the basis of the moral and political sciences.

Literature: DESTUTT DE TRACY, Éléments d'Idéologie, especially i (1808), Preface and Introd.; UEBERWEG-HEINZE, Gesch. d. Philos., III. ii. (8th ed., 1897) 36; PICAVET, Les Idéologues. (A.C.A.Jr.)

Ideo-motor: Ger. ideomotorisch; Fr. idéomoteur; Ital. ideomotore. Applied to action considered as following upon thought. It is contrasted with SENSORI-MOTOR (q.v.) and REFLEX (q.v.).

The term is sometimes limited to actions which are non-voluntary or involuntary; but the better usage includes voluntary action in the ideo-motor class. (J.M.B.- G.F.S.)

Ideoplastic (1) and Ideoplasy (2) [Gr. idea, idea, + plastoV, formed]: Ger. ideoplastisch and Ideoplasie; Fr. idéoplastique and idéoplasie; Ital. ideoplastico and ideoplasia. (1) Applied to the physiological functions considered as liable to modification from suggested ideas (used originally by Durand de Gros -- L.M.). (2) Suggestions operative in the production of physiological changes. Used by Ochorowicz (Ment. Suggestion, Eng. trans.), where the noun-form is mistakenly given 'ideoplasty.' (J.M.B., G.F.S.)

Idiocy [Gr. idiwteia, uncouthness, want of education; idiwthV, a person private or apart]: Ger. Idiotie; Fr. idiotie; Ital. idiotismo, idiozia. Deficiency in the ordinary mental powers, due to disease or failure of development of the central nervous system. More especially, idiocy often relates to the severer forms of such mental deficiency, while children of subnormal capacity or backward development are spoken of as feeble-minded, or mentally deficient children. There is some tendency to use the term feeble-minded to include all degrees of defect from the slightest to the most severe. (J.J.- J.M.B.)

Description. A general description may be profitably confined to an average case of idiocy. The typical idiot shows not merely mental, but physical defect: a blunted growth, a stooping attitude, a coarse skin, weak and flabby muscles, a sluggish circulation, a defective mastication and digestion of food, perverted or undeveloped sexual functions, a defective co-ordination of movements, a tendency to repeat a few simple automatic movements, a lowered sensibility (or sensory disorder), indistinct speech, and a general absence of alertness, with weak memory and mental initiative. Inability to take care of his person, a defective moral sensibility, and lack of appreciation of the feelings of others render the idiot socially unfit, apart from the more strictly intellectual deficiency. Variations from the type are considered below.

Frequency and Causes. The frequency of idiocy is most difficult to ascertain, owing to the unwillingness of the parents to report it, and varies markedly in different countries; certain varieties, as CRETINISM (q.v.) in Switzerland, being apparently related to local influences. General statistics indicate that one idiot to every 500 of the population is a conservative estimate, and that there are probably nearly as many idiots as insane, and more than the blind and deaf together (Ireland). Heredity or predisposing causes are most influential in the production of idiocy; physical defects being quite as pronounced as mental defects, according to the results of Shuttleworth and Beach. A phthisical family history was present in 28^.31 per cent. of the cases, inherited disease in 21^.38 per cent., and in an additional 20 per cent. a neurotic inheritance, in which epilepsy (8^.69 per cent.) was frequent. The frequency of deafness in idiots has also been noted. Parental intemperance is a prominent predisposing cause, being found in from 13 per cent. to 20 per cent. of all cases, but in as many as 38 per cent. (Kerlin) if the grandparents also be counted. Idiocy may result from shock or ill health of the mother during gestation, and is more frequently the result of accidents, &c., incidental to birth. Many accidental causes after birth (epilepsy, injury to the head, fevers, sunstroke, fright) may be inducing causes of idiocy, but it is estimated that in at least two thirds of all cases there are some marked congenital defects. These several factors frequently act in combination, the inducing cause serving only to bring to the foreground an inherited taint. It should also be noted that while in some cases idiocy is sequential to epilepsy, the epileptic tendency is a marked concomitant of idiocy, being one of the frequent degenerative stigmata of the idiotic condition.

Pathological. The appearances of gross brain defect observable in cases of idiocy comprise most of the serious abnormalities to which this organ is liable; and certain forms of idiocy have been differentiated according to the pathological cause. Idiocy may result from mere deficiency of brain substance, which is termed microcephalic; from hypertrophy of the brain, one prominent form of which is HYDROCEPHALUS (q.v.). Softening or sclerosis of the brain, tumours and affections of the membranes and blood-vessels, asymmetries of development, atrophy of the cerebellum, defects of the corpus callosum, unusual forms of cortical cells in microscopical examination, &c., have been observed. Such defects may be distinguished according as they are formative or developmental, and as they result from inflammatory or degenerative diseases.

Varieties. The classification of cases of idiocy has proceeded in part upon the time of appearance of the defect, upon the degree of intelligence retained, upon the specific pathological basis for the condition, and upon the general appearance of the case. It is thus described as congenital, developmental, and accidental; each of which, especially the first, fall into many subdivisions suggestive of their pathology. Idiocy is also described as 'true' idiocy, imbecility, weak-mindedness, &c., or as microcephalic, hydrocephalic, eclampsic, epileptic, cretinism, &c., or as Mongolian, Negro-like, Malay, &c. Practically the pathological form of classification has been most influential, the other modes of description serving as supplementary. In a measure the various forms have been correlated with physical peculiarities and psychological defects, but not sufficiently to enable any brief formulation of these to be made. For descriptions of illustrative cases the reader may be referred to the standard works cited below.

Psychological Status. Idiocy is often spoken of as a state of arrested mental development, the unfoldment of mental power being cut off at the infantile or childish state. To a large extent this is true; and, as indicated by the process of education, there is spread out over a long period the slow steps of progress usually acquired quickly, spontaneously, and almost without effort. There is, however, an unequal development which is characteristic of idiocy. Adolescent and adult instincts appear, muscular strength and skill exceeding that of childhood lead into new fields of activity, while the mere aggregation of sensory and motor experiences, however poorly assimilated, produces some differentiation. In a few cases, sometimes known as idiot-savants or idiot-geniuses (see Peterson, Pop. Sci. Mo., 1896, 237), one special group of faculties, such as music, linguistic faculty, memory, drawing, construction, is well developed, although the general mental operations are of a simple character. It is seldom that such facility is infused with great intelligence, but resembles more a freak of receptive or constructive facility. Morally, idiots are remarkably deficient; it is difficult to arouse in them the sense of shame and propriety; their love of approbation and capricious likings for certain individuals are often the most promising means of influencing their conduct. The analogy which has been drawn between the mental state of idiots and of animals, and the conception of idiocy as an atavistic condition, are on the whole misleading. In the one case the nature and direction of exercise of the intelligence is too diverse to be readily comparable, while the best authorities deny that in the character of the brain and other abnormalities of idiots atavistic tendencies are particularly marked.

Training of Idiots. The methods of educating the feeble-minded to the maximum degree of usefulness of which each is capable serve to illustrate the different degrees of defect, as well as its nature. The form of training now introduced is aptly termed physiological, and is one of the main contributions associated with the name of Seguin. It begins with the principle that a cultivation of muscular co-ordination is the necessary starting-point of the education of the feeble-minded. The apathetic torpid idiot is induced by such exercises as the throwing of a bean-bag, clapping the hands in time to music, marching, &c., to convert a simple imitative action into a purposive movement. If there is more serious defect in the movements of legs or arms, walking on flat rounds of ladders placed on the floor, to induce regularity of step, balancing exercises, grasping of blocks, placing marbles or pegs in designated holes in a board, the taking apart and putting together of boxes and simple contrivances, and other devices, are used to induce and exercise co-ordinating movements. Their senses must be aroused by the handling of objects of different textures and shapes; their ears, with which they hear but do not listen, must be excited by systematic exercises in music, rhythm, and characteristic noises. Similarly for sight, the fixation of attention, the transition from seeing to looking must be aided by such devices as the kaleidoscope, coloured balls, diagrams, pictures, drawing. The training of speech offers a wide and difficult field. Some idiots do not speak at all, or at best only a few isolated words, and comprehend only a few simple directions. In many the natural speech tendency is slight, but may be considerably developed. Some pick up speech slowly and at a later period than is normal; but few, if any, of the feeble-minded have a normal control over articulation and readiness of expression. Articulation is induced and developed by progressive exercises in the movements of tongue, lips, and vocal chords. Imitation, chorus exercises, and patient correction of faults, together with general improvement in physical power, will bring motor control; yet the use of language will always be limited to the degree of mental capacity which is present. As the subjects of such training grow older, more elaborate occupations and handiworks are open to them; perhaps 20 per cent. of them will become self-supporting, and another 20 per cent. useful and in a measure able to take care of themselves. The psychological interest in this process is its illustration of the relations between motor and mental effort, and the substitution of the slow and deliberate acquisition for the quick spontaneous self-education of normal children. Apart from mental training, relief has been obtained by appropriate medical treatment, or even surgical operation, but this only in cases when the idiocy was evidently the result of a definite pathological condition which was thus reached. Cf. IMBECILITY, and CRETINISM.

Historical. The modern phase in the study and training of the mentally defective may be said to start with Seguin, who began to instruct an idiot child in 1837, and in 1846 issued his important book on the education of idiots. Under the view which was thus displaced the idiot was considered, and often treated, as little more than a human beast, and many cases of idiocy were described as wild men, wolf-boys, and the like.

Literature: W. W. IRELAND, The Mental Affections of Children (1898); MORSELLI and TAMBURINI, in Riv. di Freniat. (1876-8); SHUTTLEWORTH, Mentally Deficient Children (1895); SOLLIER, L'Idiot de l'Imbécile (Paris, 1891), and art. Idiocy, in Twentieth Cent. Pract. of Med. (1897); LANGDON-DOWN, The Mental Affections of Childhood (1887); E. SEGUIN, Idiocy and its Treatment by the Physiol. Method (1866). (J.J.)

Idiopathic [Gr. idiopaqein, to feel for oneself alone]: Ger. idiopathisch; Fr. idiopathique; Ital. idiopatico. A term applied to a morbid condition or disease which is primary and distinctive; not a secondary effect of another disorder, nor a symptom of such disorder, nor the result of accident or injury. It thus often implies the typical and hereditary form of the disease, as idiopathic epilepsy, idiopathic insanity. (J.J.)

Idioplasm [Gr. idioV, the same, + plasma, a thing formed]: Ger. Idioplasma; Fr. idioplasme; Ital. idioplasma. The nuclear chromatin substance that forms the physical basis of heredity.

Suggested by Nägeli (Mechanisch-physiologische Theorie der Abstammungslehre, 1884). Practically equivalent to the GERM-PLASM (q.v.) of Weismann. (C.LL.M.)

Idio-psychological Ethics: Ger. idiopsychologische Ethik; Fr. morale idio-psychologique (suggested -- TH.F.); Ital. morale idiopsicologica. A theory of ethics which depends upon 'the inner facts of conscience itself' (Martineau).

The term is used by Martineau (Types of Ethical Theory, 1885), who distinguishes idio-psychological ethics from hetero-psychological ethics (that is, the theories of ethics which derive moral phenomena from other mental categories). These two classes of theories, together with the unpsychological theories (which base ethics upon metaphysical or physical doctrines), make up his classification of ethical theories. (W.R.S.)

Idio-retinal Light: Ger. Eigenlicht der Netzhaut (Augengrau, Augenschwarz); Fr. lumière propre de la rétine; Ital. luce propria della retina. The hazy or cloud-like patches of dull grey in the field of vision when the eyes are free from stimulation and after-images. Cf. Helmholtz, Physiol. Optik (2nd ed.), 242, 409, 1007.

It is important for the Helmholtz-Fechner theory of after-images (loc. cit., 502). G. E. Müller refers it to the cortex (Zeitsch. f. Psychol. xiv. 40), in order to reduce Hering's retinal 'antagonism' to the single category of 'subtractive' (with elimination of 'relative') antagonism (Ebbinghaus, Psychol., i. 259, 262). For its measurement, cf. Fechner, Elem. d. Psychophysik, i. 168. See Visual Sensation under VISION. (E.B.T.)

Idiosyncrasy [Gr. idiosugkrasia, a peculiar temperament or habit of body]: Ger. Idiosynkrasie; Fr. idiosyncrasie; Ital. idiosincrasia. Idiosyncrasy denotes peculiar reactions of the individual to certain external influences, and further implies that such response or affection is not readily correlated with known physiological or psychological principles.

The term is thus distinguished from temperament or constitution or racial characteristics, all of which are expressions of the individual's special variation in regard to the normal and regular distribution of endowment. Peculiar likes and dislikes, the special effects of sensory stimuli, the actions on the secretions and vaso-motor system, the behaviour under the action of drugs and stimulants, peculiar habits of mental work, are types of idiosyncrasies. One person has the peculiar sensation of the blood running cold at the squeezing of a dry sponge, another at the creasing of paper or the scraping of the fingernail; the odour or the mere presence of a certain animal, flower, or fruit is painfully disturbing to some individuals. In the use of drugs the normal effect at times fails to appear, and marked variations in the quantity needed to produce the same effect are readily noticeable. What is one man's meat is another man's poison; what conduces to productive mental energy in one defeats this object in another. The story of Schiller requiring the odour of decaying apples to stimulate him in his composition, or of Kant requiring the sight of a button on a student's coat to hold the course of his lectures, are cases of mental idiosyncrasies. During pregnancy and during adolescence the temporary appearance of special idiosyncrasies -- unusual tastes and susceptibilities -- is frequently observed. That many of these are somewhat imaginary in type, or partake of that peculiar admixture of feigning and reality characteristic of hysteria, cannot be doubted; but as all idiosyncrasies are expressions of the reactions of the nervous system, these are no less so. (J.J.)

Idol [Gr. eidwlon, an image]: Ger. Idol; Fr. idole; Ital. idolo. An object, usually an image or representation of a human or animal form, with which some mysterious and superhuman power is associated, and which is supposed to be propitiated by the worship paid to the object.

An immediate object of worship is not an idol, even though it may be an animal or something wholly unworthy of the religious sentiment. An idol is, in the first instance, an indirect object of worship, and is more or less symbolical. It would have its rise in the need the primitive mind would feel for some tangible symbol or representative of the mysterious objects of its worship. Idol-worship could not exist, therefore, as a primitive form of religion.

Literature: see references under FETICHISM; also SPENCER, Princ. of Sociol., i. chaps. xxi, xxii; MAX MÜLLER, Is Fetichism an Original Form of Religion?, 38, 110, 196. (A.T.O.)

Idol (Baconian). Prejudices natural to man, whether native or acquired, which hinder the discovery and advancement of truth; used first (Lat. idola) by Giordano Bruno (1582 ff.).

The list of 'idols' is given by Bacon in his Nov. Org., i. 38 ff. They are cited in concise quotation in Eisler, Wörterb. d. philos. Begriffe, 'Idol.' (J.M.B.- E.M.)

Idolatry: Ger. Abgötterei; Fr. idolâtrie; Ital. idolatria. (1) The worship of idols. Cf. IDOL.

(2) A name applied to any religious belief or worship that is conceived to be not only false but also degrading.

In the strict sense of the term idolatry is not a primary form of religious worship. It is devoted to an object which at first symbolized some unseen power, and has gradually become itself an object of superstitious regard. Image-worship is a species of idolatry in which this process is clearly manifested. The image or picture is at first merely representative, but tends gradually to become identified with the object itself. (A.T.O.)

Ignorance (in law) [Lat. ignorantia]: Ger. Unwissenheit; Fr. ignorance; Ital. ignoranza. Want of knowledge as to a certain point; lack of information as to a certain matter.

Ignorance of law: ignorance as to what the law is; as when a man, not knowing bigamy to be unlawful, marries a woman already married to another. It is a legal maxim that ignorantia legis neminem excusat.

Ignorance of fact: ignorance as to what the facts are; as when a man marries a woman already married to another, not knowing of the former marriage. The maxim is ignorantia facti excusat. Ignorance is a cause of error, but a different thing from error, which is a want of conformity between our notions of things and their real state or nature.

The Roman law placed important limitations on the doctrine that ignorance of law is no excuse. It was an excuse to minors, women, and soldiers, under certain circumstances, and a broad distinction was drawn between its effect on public and on private wrongs. It is also, in some cases, a ground for relief or of defence in courts of equity. Cf. Pomeroy, Equity Jurisprudence, ii. § 842.

Literature: PHILLIMORE, Princ. and Maxims of Jurisprudence, xix; Dig. xxii. 6, De Iuris et Facti Ignorantia; HOLLAND, Jurisprudence, chap. xiii, viii. 94; HOLMES, On the Common Law, 47; MERLIN, Répertoire de Jurisprudence, 'Ignorance'; and SOHM'S Inst. of Roman Law,  § 29, on Error in Substantia. (S.E.B.)

Ignoratio Elenchi: see FALLACY.

Illation and Illative: see INFERENCE.

Illegitimate (in law): see LEGITIMATE.

Illicit Process: see FALLACY (1), and DISTRIBUTION (in logic).

Illogical: see LOGICAL.

Illumination: see ENLIGHTENMENT.

Illusion [Lat. in + ludere, to play]: Ger. lllusion, Täuschung; Fr. illusion; Ital. illusione. (1) The construction, on the basis of data which are real in their sphere, of a mental object which is accepted as real but is not so.

(2) The mental object thus constructed.

(3) In general, mental acceptance of the unreal.

Meaning (1) -- with (2) -- is the recommended psychological definition. Illusion is thus any mistaken mental construction which has reliable data as its point of departure. The distinction from HALLUCINATION (q.v.) is twofold: (a) in hallucination, the trustworthy data are absent; that is, the determining elements in the construction are either of purely imaginative or of organic origin -- both these cases being illustrated under that topic, and both being on the border, or over the border, of the pathological. (b) Hallucination is confined to the perceptual -- to objects of sense in contrast with the DELUSION (q.v.) of higher mental processes. Illusion is thus broader, in that it covers those errors of the logical operations as well which are not of the persistence or of the indirect determination -- in a system of beliefs -- which characterize delusions.

The limits of the three terms inter se are, however, largely practical. The central processes of illusion and of hallucination, arising from organic causes, are the same; and in most cases of either, the influence of delusional elements, due to the earlier condition of mind -- notably to emotional states -- is marked. The cases of pure SENSE ILLUSION (q.v.), on the other hand, are cases really of perception, not of illusion; since they are normal, constant, and common to all individuals, and are exposed by resort to tests outside the sphere of the particular senses concerned. Cf. OPTICAL, ILLUSIONS, and ILLUSIONS OF MOTION AND MOVEMENT.

Illusions occur in connection with all the senses, and with certain obscure modes of consciousness. Cf. ORIENTATION (illusions of), and PRESENTIMENT.

Literature: BIBLIOG. G, 2, n; titles cited under HALLUCINATION; list of references in BALDWIN, Senses and Intellect, 269. (J.M.B.)

Illusion (aesthetic) or Self-illusion: see SEMBLANCE. Also cf. ART, BEAUTY, and CLASSIFICATION (of the fine arts).

Illusion (pathological). A distinction between the usual and normal sense-deceptions and the unusual and somewhat abnormal false interpretation of sensory stimuli is much to be desired. Such normal illusions are considered under the preceding topic; and the general relations of hallucinations and illusions, both in the sane and insane, are considered under HALLUCINATIONS.

Illusions in the specific sense may be illustrated from the case of the whitewashed tree, which is momentarily mistaken by the belated wanderer in a lonely road for something more mysterious; to the raving of the maniac who sees in the wall-paper patterns the spiteful faces of his persecutors, and hears in passing footsteps or everyday noises their curses and insults. Some misinterpreting mental attitude or factor seems necessary to the formation of the typical illusion; it may be expectant attention, or fear, or the preponderance of a limited train of thought, or the poisoning of the brain by opium or hashish, or the disordered reasoning of insanity. When such misinterpretations are slight, the resulting illusion is assimilated to the normal sense-deception; when it becomes more marked, and particularly when the interpretation or inferential element becomes more prominent, it passes gradually into the abnormal type, and then its aetiology and nature is quite similar to that of the hallucination. This is well illustrated in the illusions of the insane; in many of these it is difficult to decide whether there exists an illusion or a pure hallucination, correlated with sensory and bodily disorders. A patient suffering from anaesthesia believes his legs to be made of wood or glass, or that he is dead; ringing in the ears is construed into warning voices; digestive troubles lead to the belief that the patient has no stomach; peculiar head-sensations, that he is possessed by another spirit; while total strangeness of disordered sensibility may lead to the belief in a changed personality. In dreams, likewise, illusions may occur; the fancies may have a sensory starting-point; while in hypnotism such are readily suggested. Cf. also DREAMS, and HYPNOSIS. (J.J.)

Illusions of Motion and Movement: Ger. Bewegungstäuschungen; Fr. illusions du mouvement; Ital. illusioni di movimento. False interpretation of sense data, resulting in the apparent perception of motion or MOVEMENT (q.v.) where it does not exist, or in the misjudgment of some circumstance attending actual motion, such as the rate, the direction, or the object that moves.

I. MOTION. Illusions of change of place may occur in any sense which is capable of giving impressions of position; they are found most commonly in vision, touch, the muscle sense, and the equilibrium sense. If we limit the term motion to displacements which are not the manifestation of subjective or organic activity, and designate the latter by the term MOVEMENT (q.v. for the distinction), as is customary, the illusions belonging to vision and touch will fall for the most part in the first category, and those of the muscle sense in the second. In many cases the illusion arises from the combination of data of several senses.

Visual Illusions. The interpretation of the rate of motion and of its source (i.e. the object that moves) is largely relative. If the eye follow a moving body, the motion will appear much less rapid than with the eye at rest, even though the entire motion be attributed to the moving object in both cases. In a moving train, the motion is attributed sometimes to the train, sometimes to the objects that pass by; but in the latter case the rate appears much greater. A similar effect is obtained from an endless belt of figured oil-cloth revolving over rollers; when the oil-cloth is near enough to fill the field of vision, the subject attributes the motion to the field or to himself, according as his eyes follow the patterns or remain fixed. Objects seen in indirect vision appear to move more rapidly than those viewed in direct vision, ceteris paribus, owing probably to the tendency of the eye to follow the object in the latter case. If the eye be fixed on a point at rest, the latter after a time will appear to move about slightly; the motion is especially marked when the object fixated is the only clearly defined point in the field of vision; it is really due to involuntary eye movements. Exner terms the experience 'autokinetic sensations.' If the eye-ball be pressed from side to side with the finger, the objects in the field of vision appear to move; but no such interpretation occurs when the eye moves normally.

A somewhat different instance of relativity is observed in the apparatus called anorthoscope. This consists of a paper with a narrow vertical slit, which is held before one eye, and a circle slightly less in diameter than the length of the slit; when this circle is moved rapidly from side to side behind the slit, it appears as an ellipse, the horizontal axis becoming shorter as the rate is increased; when the motion is slow, the illusion disappears, or is reversed, the horizontal axis becoming longer than the vertical.

Illusions of the direction of motion may be due to a false judgment of perspective, or to the undue prominence of certain factors and overlooking of others. An example of the former appears when we observe the motion of a windmill from an oblique angle at a distance; either side of the mill may be made to appear the nearer, so that the upper vanes seem to move now towards, now away from us. A similar illusion of perspective may be observed with vessels on the water. An illusion of direction due to the obscurity of certain factors is observed when a spiral figure is rotated rapidly about its centre on a colour-wheel; the rotary motion is indistinguishable, and there appears instead a motion of all points of the spiral towards the centre, or away from it, according to the direction of rotation. If a card with a number of broad concentric circles like a target be moved in a circle before the eyes without rotation of the card, the figure becomes partly blurred, and the blurred sectors appear to rotate in the direction of the actual movement. If a figure consisting of a circle with teeth projecting inwards or outwards (like cogs) be moved in a similar manner, the cogs will appear to rotate around the circumference of the circle. Figures of this sort are known as strobic circles.

The illusion of rest is illustrated in a rapidly rotating wheel, whose spokes present the appearance of a continuous, motionless, and semi-transparent surface. In the thaumatrope different pictures or letters are printed on the two sides of a card, which is rotated by twirling two strings attached to the right and left edges; the two pictures combine into one, or the letters into words, which appear to remain stationary before the eyes. An opposite illusion appears in the stroboscope. This consists of a circular card with a number of axial slits, and another circular card, placed behind it, with a series of dots or figures placed around the circumference, representing different phases of an object in motion. The two cards may be rotated in the same or in opposite directions; looking through the slits as they pass, we catch momentary glimpses of the successive images, and when the rotation is rapid they appear as a single object having a continuous motion. The figures may be placed on the back of the first card, and reflected by a mirror, which is substituted for the second card. There are various forms of stroboscope, called dedalium, phenakistoscope, zoetrope, &c. In the zoetrope the slits are cut in the side of a short cylinder, like the cover of a bandbox, while the figures are on a strip, which is placed upright around the inside of a cylinder; with a series of instantaneous photographs a very realistic appearance of continuous motion is obtained. In these forms of stroboscope the pictures must be the same distance apart as the slits. Recent applications of the stroboscopic illusion are found in the kinetoscope, mutoscope, vitascope, cinematograph, biograph, &c. Here the pictures follow one another in rapid succession, remaining in view for a period which is much longer than the time occupied by the transition; the latter is so short as to make the real motion imperceptible, while the pictures at rest are clearly perceived; this avoids the necessity of slits. The pictures represent very near phases of motion, and the result is an illusion of motion which is perfect in proportion to the degree of perfection of the apparatus; the rate of the illusory motion may be made the same as in life. The pictures may be enlarged and projected upon a screen by means of a lantern.

With certain coloured diagrams a continuous to-and-fro motion gives rise to the appearance of a sudden springing of the figures from side to side; this illusion is known as the 'fluttering heart,' or chromatokinopsia.

Similar is the so-called Münsterberg-Jastrow phenomenon. A circular disk with sectors of two alternating colours is rotated rapidly, while a pencil or thin stick is moved to and fro in front; alternate bands of the colours on the disk appear in place of the blurred image of the pencil; the width of the bands varies with the rate of motion.

After-images play a part in some of the above illusions, and give rise to others. In connection with the spiral illusion cited above, a distinct after-image may be observed; if the figure be suddenly brought to rest, motion in the opposite direction appears to set in and to continue for some time. An after-image illusion of motion in the same direction may also be observed; if a moving object be regarded for a time with unmoving eyes, and the eyes be suddenly closed, an after-image will appear, which seems to move onward for a brief period.

Tactile Illusions. These occur usually in connection with active touch, and combine with the illusions of muscular movement to be described later. In some cases, however, they arise independently. If a string be drawn through the subject's fingers by another person, it seems to be longer when drawn slowly than when drawn rapidly; that is, the amount of motion appears greater in the former case. An object passing over the finger-tips, forehead, &c., gives rise to an impression that the member in question is also moving, but in the opposite direction. Illusions of direction, more or less marked, are often observed in objects moving over the skin. Tingling is often interpreted as motion of something upon the skin.

II. MOVEMENT AND BODILY POSITION. Muscle Sense Illusions. Our judgment of the rate and direction of muscular movement is very accurate. It is noted, however, that an object appears heavier as the rate of lifting is slower. When the member moved is seen, not directly, but in a mirror, the visual impression of direction may supplant the muscular, so that the member is felt to move in the same direction as the reflected image. In Stratton's experiment, in which the visual field was entirely reversed by lenses worn over the eyes, the location and direction of muscular movement came gradually to conform to the new visual field.

When one part of the body is moved over another (e.g. the finger over the forehead), the movement may be referred to the wrong source, or both members may appear to join in the movement. In the similar tactile illusion mentioned above, there is often an illusory muscular sensation present also. The removal of resistance to one set of muscles may be interpreted as a force applied to the antagonistic set. If a string bearing a heavy weight be held in the subject's hand, with closed eyes, and the weight be suddenly pulled upward by another person, the subject's hand tends to fly up, and the movement is attributed to the application of an outside force. A similar illusion is observed in pouring water from a pitcher; the constant loss of weight from the escaping water is involuntarily interpreted as a force resisting our effort to lower the mouth of the pitcher.

An illusion regarding the amount of movement executed may arise when part of the movement is unconscious. If the head be turned to one side, with closed eyes, and an attempt be made to point at a given object in front of the former position, an error in direction is observed, owing to the unconscious 'lagging' of the eyes when the head is turned. Unconscious eye movements are responsible for several of the visual illusions described above. Where one of the eye muscles is partly paralyzed, movement of the eyes in that direction is exaggerated.

Another muscular illusion arises from the tendency of the two hands to assume symmetrical positions. If one hand be placed somewhat higher than the other, and we attempt to describe equal downward movements with both hands together (with eyes closed), the higher hand tends to make the greater movement, so as to approximate the level of the other. This tendency to symmetry has definite limits, however; if we endeavour to bring the hands together in front of the body, one is constantly found to be slightly higher or further out than the other.

An illusion of movement in an immovable member is noted if one hand be placed, palm down, with the last three fingers resting flat on a table, and the forefinger bent under and resting against the side of the table; after the forefinger has been bent in as far as possible, a sensation of apparent movement can still be felt if an effort be made to bend it further.

Equilibrium Sense Illusions. Although muscular and visual sensations are important data in affording knowledge of the passive movements and position of the whole body, the basis of these sensations is the special sense whose organs are the semicircular canals of the ear. The illusions connected with these sensations are due for the most part to the rapid fatigue of the equilibrium sense, and to faulty combination of its data with the visual and muscular.

The chief motor illusions of the equilibrium sense are observed with the 'rotation table.' This consists of a long, flat board, on which the subject lies, and which is made to rotate in the horizontal plane. If the subject's eyes remain closed, and a uniform rate of rotation be maintained, the movement gradually appears to become slower, and finally to stop; if the table now be actually stopped (or nearly so), the subject will experience an illusion of movement in the opposite direction. The same illusions appear in connection with progressive movement in any direction; but in experiences of the latter sort, the effects are usually masked by the jolts or vibrations which accompany the motion, and which are interpreted in terms of movement forward or backward. In a railway train, for example, the sense of movement proper is lost soon after the train attains its speed; but by closing the eyes we still feel the train to be moving at the same rate, either forward or backward. The character and frequency of the jolts give the clue to the speed, so that in travelling over a smoother road-bed than usual we tend to underestimate the rate of progress, and vice versa. The illusion of reversal in progressive movement may be assisted by vision, if we look in a mirror placed perpendicular to the direction of motion; but when the train makes a curve the two senses part company; the equilibrium sense then asserts itself, and the landscape appears to fly around in the same direction as the train. If the train slows up while the illusion of reversal is being experienced, the muscular data become prominent, and the train appears to be going uphill, and vice versa. The equilibrial and visual data may be combined as follows. The subject is stretched at full length on the rotation table, with head slightly raised; the room is darkened, so that some vertical white strips on the dark wall are barely visible. If, then, a mirror be placed before him, which rotates with the board, so that the strips seen in front (being really behind him) appear to move in the same direction as his feet, the rotation is interpreted as progress sideways, in the direction in which the head actually moves; that is, the data of the equilibrium sense serve for the head only, while the reversed visual data make the feet appear to move in the opposite direction from the true one; this is direct evidence of the location of the equilibrium sense in the head.

The feeling of dizziness that ensues upon rapid rotation is (apart from the nausea connected with it) a phenomenon of the equilibrium sense; the illusion of motion that constitutes dizziness is the after-image belonging to this sense. A muscular-visual illusion is present also when the movement has taken place with open eyes; the objects in the field of vision appear to continue moving after the subject ceases to rotate. This is known as Purkinje's dizziness; it is due to unconscious eye movements. A kindred illusion, due to the unconscious control of the muscles through the equilibrium sense, is illustrated in a well-known parlour diversion. The subject stands with his body bent forward from the hips and his head resting on a cane which extends vertically from the floor; he walks around the cane three times, then raises his head and attempts to walk across the room, with the result that he staggers and usually falls. The equilibrium sense has been adjusted to the rotary horizontal movement, and this is suddenly transformed into a sense of vertical rotation when he rises; in his involuntary muscular adjustments to this supposed motion he is thrown over in the opposite direction. The illusion of rocking which is experienced on land after an ocean voyage is due to the same cause. In the haunted swing illusion, the subject is seated on a swing in a perfectly closed room; the swing remains stationary, while the entire room moves like a pendulum. The motion is attributed to the swing. The feeling of dizziness is very marked.

Illusions concerning the position of the body as a whole arise when the visual and muscular data are withdrawn or greatly altered. If the subject be strapped to the tilt-board and blindfolded, any rotary motion in the vertical plane is perceived almost wholly by the equilibrium sense, whose data are thus exaggerated, any deviation from the horizontal appearing much greater than it actually is; this is more noticeable in the uncommon positions, with head lower than the feet, the head seeming to point directly downward when the actual angle is 45^o or more short of that position. An illusion of position arises also when only the visual data are withdrawn. If the subject stand with closed eyes, and throw his head backward, forward, or on to one shoulder, his judgment of position, measured by a rod held in what he considers a horizontal line in the plane of his movement, will show a constant error; the inclination of the rod is usually contrary to the direction of his movement. (H.C.W.)

Literature: visual illusions: SANFORD, Course in Exper. Psychol., expts. 128, 134, 159, 222-31, and references there given; HELMHOLTZ, Physiol. Optik, 2. Aufl., 494, 498, 533, 711, 749, 763, 770 (full descriptions of apparatus and methods); STERN, Zeitsch. f. Psychol. (1894), vii. 321-86; MACH, Analysis of Sensations (Eng. trans.), 69 (oil-cloth illusion); EXNER, Zeitsch. f. Psychol. (1896), xii. 313-30 (autokinetic sensations); ZÖLLNER, Pogg. Ann. (1862), cxvii. 477-84 (anorthoscope); S. P. THOMPSON, Brain (1880), iii (strobic circles); SCRIPTURE, New Psychol., 108-20 (stroboscopes, kinetoscope, &c.). Tactile and muscle sense illusions: SANFORD, Course in Exper. Psychol., expts. 5, 12, 36-45, and references; STRATTON, Psychol. Rev. (1897), iv. 341, 463 (visual reversal). Equilibrium sense and dizziness: SANFORD, Course in Exper. Psychol., expts. 46-51, and references; MACH, Grundlinien d. Lehre v. d. Bewegungsempfindungen, 83, 128; DELAGE, Physiol. Stud. ü d. Orientirung (deutsch v. Aubert); PURKINJE, Ueber d. Schwindel (repr. by Aubert with above); WARREN, Psychol. Rev. (1895), ii. 273; WOOD, Psychol. Rev. (1895), ii. 277. Apparatus for visual illusions, in Milton Bradley Co.'s 'Pseudoptics,' section D. (H.C.W.- E.C.S.)

Illusions of Orientation: see ORIENTATION (illusions of).