DICTIONARY OF
PHILOSOPHY AND PSYCHOLOGY

Inebriety [Lat. in + ebrietas, drunkenness]: Ger. Trunkenheit; Fr. inébriété; Ital. ebbrezza, ubbriachezza. The effects of an over-indulgence in alcoholic liquors, either occasionally or habitually.

General drug intoxication is considered under PSYCHIC EFFECTS OF DRUGS (q.v.), and the special effects of indulgence in alcohol under ALCOHOLISM (q.v.). Inebriety is often used in reference to the medico-legal relations incidental to actions committed by persons in a more or less irresponsible condition through alcoholic indulgence. (J.J.)

Inertia (nervous) [Lat. inertia, lack of skill or activity]: Ger. Trägheit; Fr. inertie; Ital. inerzia. A name applied, by physical analogy, to that peculiarity of nervous substance, or of a particular sense-organ, which conditions the 'rise' and 'fall' of sensation; i.e. the fact that the sensation requires an appreciable time to reach its maximal clearness, and an appreciable time to disappear, after the presentation and the removal respectively of the stimulus.

Some of the facts of inertia are as follows: (1) The interval separating the 'primary' and 'secondary' pressures from the skin may be due to the inertia of the central grey matter of the cord (Godscheider, 'Verh. d. physiol. Gesell. zu Berlin,' 1890, in Arch. f. Physiol., 1891, 168 f.; Sanford, Course in Exper. Psychol., expt. 11, and cf. expt. 32; but see von Frey, Abhandl. d. kgl. sächs. Gesell. d. Wiss., 1896, 243; Külpe, Outlines of Psychol., 85, 92). (2) Initial and terminal inertia can be demonstrated in the case of the auditory apparatus (Sanford, op. cit., expt. 64; Stumpf, Tonpsychologie, i. 16, 211 f., 277, 391; ii. 516 f.; Urbantschitsch, Pflüger's Arch., xxv. 323 ff.); (3) and in that of the visual (Fick, in Hermann's Handb. d. Physiol., iii. 1, 211; Sanford, op. cit., expt. 144; Ebbinghaus, Psychol., 230, 241; Helmholtz, Physiol. Optik, 2nd ed., 530 ff.; Fechner, Pogg. Ann., x1v. 227 ff.; Brücke, ibid., 1xxxiv. 418 ff.; Exner, Pflüger's Arch., iii. 214 ff.; Aubert, Physiol. Optik, 560; Rood, Colour, 92 ff.; Amer. J. of Sci., 1860, Ser. 2, xxx. 182 ff.; Nichols, ibid., 1884, Ser. 3, xxviii. 243 ff.; Charpentier, C. R. de l'Acad. d. Sci., cxiii. 147 ff., 217 ff.; cxiv. 1423 ff.). (4) The length of reaction-time to smell, taste, and temperature may be due in part to initial inertia of their organs (Wundt, Physiol. Psychol., 4th ed., ii. 317). (5) Cutaneous pain shows an initial inertia as compared with cutaneous pressure (Sanford, op. cit., expt. 32; von Frey, Ber. d. kgl. sächs, Gesell. d. Wiss., 1894, 294). (E.B.T.)

Inertia (in physics): Ger. Trägheit, Beharrungsvermögen; Fr. inertie; Ital. inerzia. That property of matter by virtue of which it does not, even when free to move, change its velocity per saltum under the influence of a force, but continually resists the change which the force tends to produce, so that the force must persist in order to effect a change.

Inertia affords the absolute measure of the mass of a body, and seems to be absolutely invariable. The use of the term in physics has therefore been deemed unnecessary, since it may be avoided by the use of the word 'mass.' Maxwell compared the resistance expressed by it to a supposed resistance of coffee to the sweetening power of sugar, since the necessity of adding more and more sugar to make the coffee sweeter and sweeter is analogous to the necessity of employing more and more force to make a body move faster and faster. This is, however, misleading, since the resistance is not in the coffee; but the fact illustrates WEBER'S LAW (q.v.) of the relation of stimulus to sensation. Yet the use of the term may be justified, as introductory to the conceptions of the fundamental laws of force and motion, and as being, at worst, quite harmless. (S.N.- J.M.B.)

Infallibility [Med. Lat. infallibilis, not liable to mistake or error]: Ger. Unfehlbarkeit; Fr. infaillibilité; Ital. infallibilità. (1) Of the Church: the doctrine that the Church, as a whole, by reason of the indwelling Divine Spirit, is rendered inerrant in matters of faith and teaching.

(2) Of the Pope: the doctrine that the Pope, when he speaks ex cathedra, is, through the divine assistance promised him in blessed Peter, endowed with inerrancy in defining doctrine about faith and morals.

The infallibility of the Church, in the sense defined, has been held from the beginning by the Roman Catholic Church, its warrant being such passages as Matt. xxviii. 20; John xiv. 16; 1 Tim. iii. 15. The Protestant churches as a rule reject the doctrine or hold it in a very much modified form. The infallibility of the Pope, though not foreign to the belief of the Church, was authoritatively enunciated for the first time by the Vatican Council of 1870. Infallibility should be distinguished from impeccability, which it does not involve, and it is to be construed as an official rather than as a personal prerogative.

Literature: MANNING, The True Story of the Vatican Council (London, 1877); WENNIGER, Apostolical and Infallible Authority of the Pope (1874); GLADSTONE, The Vatican Decrees, &c. (1874), also Vaticanism (London, 1875); DÖLLINGER, Über die Unfehlbarkeitsadresse (1870); REINKENS, Über päpstliche Unfehlbarkeit (1870); GUERANGER, De la Monarchie Pontificale (1870). (A.T.O.)

Infancy [Lat. infans, infant]: Ger. (1) Kindheit; Fr. (1) enfance; Ital. (1) infanzia. The period of immaturity during which the individual is dependent on parental care; it extends (1) from birth to the period of self-support (in a biological sense); and (2) to maturity or self-support (in a social, legal, and economic sense).

(1) The origin and meaning of infancy is an important biological problem. >From the point of view of evolution, especial significance attaches to this period. It is thought to have arisen correlatively with the parental instincts in the animal world, and to have direct relation to the GESTATION (q.v.) period; indeed the term infancy is sometimes used to cover both periods, a division being made between the intra-uterine (gestation or prenatal) period and the extra-uterine (postnatal) period. The relation of these periods is somewhat thus: a relatively short prenatal period is correlated with swift embryonic development in creatures which are born equipped for immediate or very early independent self-support. The extreme case is found in those insects which are born practically adult or fully developed. On the other hand, a relatively long post-natal infancy goes with relatively long and slow embryonic development, relative immaturity at birth, and relatively complex nutritive and protective adaptations for the young after birth. The significance of this is that by this arrangement higher endowments, involving plasticity, intelligence, complex social relationships, &c., are made possible; for the young, not having to begin immediately at birth to take care of themselves, need not have the fixed instinctive and reflex nervous and other special adaptations, but may have the general capacity for learning by slow accommodation to a varied set of conditions, while nourished and protected by their parents. The infancy period, therefore, adds directly to the resources of the species for the production of individuals of a higher order. With this goes the evolution of the brain in quality and complexity in the grey matter, with its convolutions and differentiations of function. Stated in terms of heredity, the meaning of it seems to be that by having an infancy period the individual may inherit less and acquire more -- have less fixity and more EDUCABILITY (q.v.).

(2) See INFANT (in law).

Literature: FISKE, Cosmic Philos.; MILNESMARSHALL, Biol. Lectures, xiii; BALDWIN, Ment. Devel. in the Child and the Race (from the psychological point of view). (J.M.B.- C.LL.M.)

Infant (in law): Ger. Unmundiger; Fr. mineur; Ital. minore, minorenne. One not of full age.

Full age in the United States and England is twenty-one years. Infants cannot bind themselves by contract, except for necessaries of life. For acts of violence or wrong they are civilly responsible. An infant under seven years of age is incapable of committing a felony.

By the older Roman law, infancy, so far as the right of control over property was concerned, ended at puberty; later the tutor, who till then had charge of an infant sui iuris, was replaced by a curator, the time of full majority being twenty-five. (S.E.B.)

Infant Psychology: see CHILD PSYCHOLOGY.

Inference [Lat. in + ferre, to bear]: Ger. Schliessen, Schluss; Fr. inférence; Ital. illazione (conclusione). (1) In logic: (a) the act of consciously determining the content of a cognition by a previous cognition or cognitions, in a way which seems generally calculated to advance knowledge.

In this sense the word differs from REASONING (q.v.) only in referring strictly to a single step of the process, or to what seems a single step. Unless the act is consciously performed, no logical control can be exercised; and this is sufficient reason for separating such acts from any operations otherwise analogous which may take place in the formation of percepts. To be conscious of determining a cognition by another, and not merely of making the one follow after the other, involves some more or less obscure judgment that the pair of representations, the determining and determined, belong to a class of analogous pairs, so that a general maxim is virtually obeyed in the act. There is, besides, a purpose of learning more of the truth. The representations concerned in inference are, it appears, always judgments (or propositions). Probably, if a pair of percepts were, in the very act of determining the one to accord with the other, looked upon as special cases of a class of pairs of percepts so related to one another that if one were true the other ought to be accepted, they would, ipso facto, become judgments.

(b) A pair (or larger set) of judgments, of which one (or all of them together but one) determines the remaining one, as in (a) above, the whole set being regarded as constituting together a cognition more complete than a judgment.

In this sense, inference is synonymous with argument. The latter word, it is true, only implies that the set of propositions might be thought, being perhaps written down and no longer even accepted by the author, while the former word implies that the movement of thought takes place. Moreover, an inference creates belief in the mind that makes it, while an argument may be a system of propositions put together with a view of creating belief in another mind, or perhaps merely to exhibit the logical relation between different beliefs. But these distinctions often vanish or lose all importance. When the determining judgment is a copulative proposition, its members may either be called the premises, or their compound may be called the PREMISE (q.v.). But when different beliefs are brought together in thought for the first time to form a copulative judgment, the premises must be taken as plural.

Several other logical meanings are in general use as more or less permissible inaccuracies of language. Thus, the determined judgment, or conclusion, may sometimes be conveniently called an 'inference.' The popular use of the word for a dubious illation, as in such a sentence as 'This is a proof positive, while that is only an inference,' is quite inadmissible. (C.S.P.)

(2) In psychology: the determination in the form of judgment, and as belonging to a mental whole, of any of the relations involved in that whole.

The matters of psychological interest are (a) the passage of consciousness from the antecedent to the subsequent or inferred content, covering the two cases of mediate and immediate inference, according as there are or are not elements common to both contents which serve explicitly to carry the mind over from one to the other and so determine them both in one whole. Immediate inference -- e.g. John is human, therefore John is mortal -- is the isolating in judgment of a phase of analysis of the whole 'human.' The humanity of John is analytically judged to involve his mortality. In mediate inference -- the forms of reasoning involving a middle term -- there are several cases, concerning all of which the question arises as to whether, from the psychological point of view, a reduction to the immediate form is possible. In the universal affirmative syllogism -- e.g. John is human, all human beings are mortal, therefore John is mortal -- we have no new psychological act or function; the process is, however, one of different emphasis, for the two contents, John and mortality, before not consciously judged in one whole, are explicitly joined, by an act of judgment, through the assertion of the minor premise. This distinction is more evident in cases of particular and hypothetical reasoning. See what is said of the 'conceptual interpretation' of judgment under ANALYTIC AND SYNTHETIC JUDGMENTS.

The various forms of inference, SYLLOGISM (q.v.), dialogism (a disjunctive conclusion following from a single premise), &c., fall in general under one or other of these headings, mediate or immediate.

(b) The other psychological point of discussion is that of so-called 'unconscious inference': the application of the term inference to the cases of mental construction or determination of objects as psychically immediate which are psychologically or logically mediate. Cf. PSYCHIC AND PSYCHOLOGICAL, and IMMEDIATE AND MEDIATE. The theory of unconscious inference was propounded by Helmholtz (Die Thatsachen in d. Wahrnehmung, and Physiol. Optik, 1st ed.) to explain colour contrast, was used in the theory of 'unconscious judgment' and in the explanation of optical illusions by Wundt (Physiol. Psychol., 1st ed.) and others, and made much of by Binet (Psychol. de Raisonnement, Eng. trans., 1899). It is now largely obsolete. The ordinary processes of perception which cover these phenomena do not yield explicit judgments of relation; and the theory of inference is now constructed rather on the basis of mediate inference as type. It would be well to follow this tendency of usage. The psychological questions are brought to full consciousness in the theory of the thought function as the progressive determination of concepts as wholes. For the distinction between INDUCTION and DEDUCTION as forms of inference, see those terms. A little-used synonym for inference is Illation. Cf. also PROBABLE INFERENCE, and PROBABILITY.

Literature: see REASONING, and BIBLIOG. C, 2, p, q; especially the general works on logic (e.g. WUNDT, SIGWART) and on psychology (e.g. STOUT, Analytic Psychol., Bk. II. chap. vi; BALDWIN, Senses and Intellect, chap. xiv). (J.M.B., G.F.S.)

Infidelity [Lat. in + fides, faith]: Ger. Unglaube; Fr. infidélité; Ital. infedeltà. (1) Denial or rejection of the distinctive tenets of any religion.

(2) More specifically, the denial or rejection of the distinctive tenets of Christianity, and particularly its claims as a divine revelation.

In view of the etymology of the word, infidelity is to be carefully distinguished from moral obliquity, which may accompany it, but is not necessarily implied in it. Again, it must be distinguished from such terms as atheism, deism, agnosticism, naturalism, and rationalism, with which it may or may not coincide, but with which it is neither generally nor specifically identical. It must also be distinguished from scepticism, of which, however, it is a species. The term infidelity is so closely associated in the popular belief with moral depravity, that its employment in cases of simple doctrinal unbelief is rarely justifiable.

Literature: PEARSON, Infidelity, its Aspects, &c. (1860); CHRISTLIEB, Christianity and modern Unbelief (Ger. and Eng.); FARRAR, Crit. Hist. of Free Thought (1863); McClintock and Strong's Cyc. of Bib. and Eccles. Lit., 'Infidelity'; Schaff-Herzog's Encyc., 'Infidelity.' (A.T.O.)

Infinite (the) and the Finite [Lat. in + finis, end]: Ger. unendlich; Fr. infini; Ital. infinito. The object of the notion of infinity (see INFINITE, notion of), considered as having independent reality, is the infinite; all other mental objects are, in opposition to it, in their mode of reality, finite.

The infinite has played an important part in the history of thought in certain connections: (1) the discussion as to the sort of reality the notion of the infinite carries with it. Here we have the views that (a) the infinite is an intuition having direct cognitive validity, or realized by mystic contemplation; (b) it is thought as the perfect, and so must have existence (its being in intellectu is also being in se, Anselm: see ONTOLOGICAL ARGUMENT, and THEISM); (c) it is an 'idea of the reason' (Kant), and so a noumenon or rational presupposition of the phenomenal world. (2) The discussions of RELATIVITY OF KNOWLEDGE (q.v.); see also RELATIVE AND ABSOLUTE. (3) The discussions of the antithesis of finite and infinite, notably with reference to the implication of an infinite being or experience in finite experience; particularly in later metaphysical discussions of an idealistic sort. See IDEALISM, and THEISM. (4) The discussion of the ABSOLUTE (q.v.) conceived as all-comprehensive and so transcending all limitation (Spinoza). (5) The theories of Agnosticism (see UNKNOWABLE), which either (a) deny the conceivability of the infinite (pure empiricism, Lewes); or (b) treat the infinite as an unknowable absolute (Hamilton, Spencer). (6) In the discussions of REALISM and NOMINALISM (q.v.). (7) In discussions of TIME, SPACE, and the WORLD (see those terms).

Little has been done in the way of utilizing the mathematical conceptions of LIMIT (q.v.) and INFINITESIMAL (q.v.) -- see also INFINITE (in mathematics) -- in philosophical discussion. The logical pitfalls of the subject are illustrated in the arguments of Zeno, the Eleatic, concerning infinite divisibility, and in the 'first antinomy' of Kant (cf. KANTIAN TERMINOLOGY, 21).

Literature: recent books on METAPHYSICS and EPISTEMOLOGY (see those topics; also BIBLIOG. B, 1, c, d), especially COHN, Gesch. d. Unendlichkeitsprolems; BRADLEY, Appearance and Reality; ROYCE, The World and the Individual; ORMOND, Foundations of Knowledge; LADD, Philos. of Reality; RÉCÉJAC, The Bases of the Mystic Knowledge; FULLERTON, The Infinite. (J.M.B.)

Infinite (in mathematics). A quantity considered as always greater than any quantity to which we assign a definite value, and therefore itself having no definite value or boundary.

Such a quantity is used in investigation as an auxiliary one, to discover relations between other quantities in certain special cases. See INFINITESIMAL. (S.N.)

Infinite (notion of) and Infinity. The conception of any sort of mental object as having quantity which cannot be exhausted by any succession of experiences, however prolonged. Such an object is said to have infinity.

This definition is intended to assign the least that can be involved in any conception of infinity. A not uncommon way in which the child first forms this conception is by imagining himself as falling over the 'edge of the world' into empty space. He sees at once that if no physical obstacle exists, there is no reason why he should ever cease falling. When reflective analysis comes into play, the mere thought that there is 'no end' is completed by the insight into the reason why there can be 'no end.' Space, for instance, is seen to be endless, because any spatial boundary is a boundary between parts of space, and therefore implies space beyond it. So the number-series is seen to be constituted by a process which at every step supplies the conditions essential for its own repetition.

The usual phrase 'idea of the infinite' is not strictly exact. Notion or concept of the infinite is better. Cf. INFINITE (in mathematics), and INFINITESIMAL. (G.F.S.- J.M.B.)

Psychologically, the infinite is a LIMITING NOTION (q.v.) on the side of quantity, its correlative limiting notion being the infinitely small; a conception used in mathematics under the term INFINITESIMAL (q.v.). It is always thought in connection with a qualitative determination to which the attribution of infinity is confined. It is different from the metaphysical notion of the absolute in this restriction to a sphere of application which makes the infinite always a general. Spinoza's doctrine of the 'infinitely infinite' is a second generalization of infinites, in which again the limiting notion of infinity is of a quantitative (numerical) series, each term of which is a qualitative determination itself quantitatively infinite. This possible generalization of quantitative infinites is well represented by Spinoza's figure of an infinite number of infinite lines, making up one of an infinite number of infinite planes, which in turn constitute an infinite sphere; such a sphere being the limiting notion of three-dimensional space. Hamilton (Logic, iv), following Descartes, distinguishes the infinite from the 'indefinite' (that whose limits are not determined). (J.M.B., G.F.S.)

Infinitesimal (in mathematics): Ger. infinitesimal; Fr. infinitésimal; Ital. infinitesimale. Denoting a quantity considered as always less than any quantity to which we assign a definite value, and therefore indefinite in value. Such a quantity is used in mathematics as an auxiliary one to discover relations between other quantities in certain special cases. See FINITE (in mathematics).

Quantities are not conceived in mathematics as having absolutely infinite or infinitesimal values. Quantities are compared by comparing their boundaries, and in all operations upon them, qua quantities, they are conceived as bounded. But infinite quantities have no boundaries, and therefore can neither be compared together nor operated on with definite results; and the attempt to do so often leads to contradictory or fallacious conclusions. For example, if a particle falls towards an immaterial centre attracting it as the inverse square of the distance, it would, on reaching the centre, be acted on by an infinite force. In such a case we can equally prove that it would pass through the centre, or that it would return from it on the straight line by which it fell. An absolutely infinitesimal quantity would be one smaller than any quantity whatever, and therefore simply zero, as an infinitesimal line would be, at most, a point, and therefore not a line at all. In attempting to use such quantities we are met by the antinomy of Kant and Hamilton, that we can neither conceive of space and time as absolutely unbounded, nor yet as having boundaries. The difficulties thus arising are completely evaded by a mathematical method of using infinites and infinitesimals in the way we have defined them.

Their use grows out of the inapplicability of the ordinary methods of reasoning about finite quantities to the case of continuously varying quantities. We can compare two straight lines by bringing them into coincidence. If we have two polygons of any number of sides, however great, we can divide them into triangles, and measure the area of these triangles. But we cannot divide a circle or any other curve into measurable parts, nor divide two different curves into congruent parts. Arithmetical numbers express only fixed quantities, not continuously varying ones. In all such cases we have, when attempting to apply ordinary methods of reasoning, to deal with an infinite number of quantities, each infinitesimal. These are treated by the method of LIMITS (q.v.). (S.N.)

Infinity (in mathematics): Ger. Unendlichkeit; Fr. infinité; Ital. infinità. That region of space or quantity which we treat as being or lying beyond all limits whatever. A line is said to extend to infinity when it extends without end, a point to be at infinity when its distance is infinite, and a quantity to increase to infinity when it increases beyond all assignable limits. Cf. INFINITE (in mathematics), and INFINITESIMAL. (S.N.)

Infinity (in philosophy): see INFINITE AND FINITE (the), and INFINITE (notion of).

Inflammation [Lat. inflammatio, a burning]: Ger. Entzündung; Fr. inflammation; Ital. infiammazione. Diseased condition of an organ or part characterized by swelling, pain, and discolouration -- generally redness -- and disturbed function.

The above results are in the main due to certain abnormal conditions of the blood-vessels, which permit passage through their walls of great quantities of lymph (swelling) and also of blood corpuscles (discolouration). (C.F.H.)

Inflation [Lat. inflatio, a blowing up]; Ger. Uebermass, Inflation; Fr. extension de (papier-) monnaie; Ital. espansione dell' emissione. An increase of debased currency beyond the amount of the better currency which it displaces (see GRESHAM'S LAW), resulting in depreciation.

'A permanent excess of the circulating money of a country, over that country's distributive share of the money of the commercial world, is called inflation' (Walker). (A.T.H.)

Inflection [Lat. inflexus, bent]: Ger. Inflexion; Fr. inflexion; Ital. inflessione. The general term including all the various modifications in the form of a word by which its relations to other parts of a proposition are expressed.

In the 'isolating' languages (Chinese, &c.), relations, if not indicated by distinct form-words, are left to be inferred from context or word-order; in the 'agglutinative' languages (Turkish, &c.), relations are indicated by elements which combine with the substance words and form composites in which the constituents maintain a consciously distinct existence; in the 'inflectional' languages the relations are expressed by changes in the word, generally of the ending. (B.I.W.)

Influence [Lat. in + fluere, to flow]: Ger. Einfluss; Fr. influence; Ital. influenza. That which enters in any way into the determination of a thing (1) is an influence, (2) has an influence, (3) exerts an influence; that is, the influence is (3) an element in the determination, (2) the capacity to contribute this element to the determination, (1) the thing which has such a capacity.

This term is useful from its very generality and vagueness; it applies to physical forces, mental elements, moral and social factors of change. (J.M.B.)

Influxus Physicus [Lat.]: see INTERACTION, and MIND AND BODY. Cf. also OCCASIONALISM, passim.

Infralapsarianism [Lat. infra, within, + lapsus, a fall]: Ger. Infralapsarianismus; Fr. infralapsarisme; Ital. infralapsarianismo. The doctrine that God's decree in relation to the fall of man was permissive and in view of the divine foreknowledge of that catastrophe.

Infralapsarianism is to be distinguished from supralapsarianism, which represents the decree as logically prior to the foreknowledge; also from sublapsarianism, which practically denies the decree and regards God's relation to the Fall as simply one of foreknowledge. Infralapsarianism is the doctrine of moderate Calvinists, while a few high Calvinists have held to the supralapsarian doctrine. Sublapsarianism belongs to a point of view that is essentially hostile to Calvinism. The doctrine of the Fall usually stands second in a series of divine determinations: (1) to create the world, (2) to permit the fall of man, (3) to elect a portion of the fallen to salvation, (4) to send Jesus Christ for their redemption, (5) to leave the residue to perish in their sins.

Literature: Schaff-Herzog Encyc. (sub verbo); JACKSON, Concise Dict. of Religious Knowledge; McClintock and Strong's Bib. Encyc., 'Sublapsarianism'; HEGENBACH, Dogmengeschichte (3rd ed.), t589; SCHNEITZER, Ref. Dogmatik, ii. 129 f.; HODGE, System. Theol., ii. 319-20; SHEDD, Dogmatic Theol., i. 441-3. (A.T.O.)

Inherence [Lat. inhaerere, to stick to]: Ger. Inhärenz; Fr. inhérence; Ital. inerenza. The relation which properties or accidents are thought to sustain to the substances to which they belong. See SUBSTANCE. (J.M.B.)

Inheritance (or Heritage) [Lat. in + haeres, heir]: Ger. (1) Erbschaft, (2) Erbtheil; Fr. héritage; Ital. eredità, retaggio. That which is inherited (1) physically; (2) socially or legally, that is, figuratively.

Sometimes used loosely as equivalent to HEREDITY (q.v.). See also GALTON'S LAW (of ancestral inheritance). (J.M.B.)

Inhibition (mental) [Lat. inhibere, to restrain]: Ger. psychische Hemmung; Fr. inhibition mentale; Ital. inibizione mentale. Inhibition exists in so far as the occurrence of a mental process prevents the simultaneous occurrence of other mental processes which might otherwise take place.

There are two distinct conditions which may give rise to mental inhibition -- conflict and competition. In conflict there is intrinsic incompatibility between two processes. Thus I cannot judge the same thing to be at once black and white. This is sometimes called, in the case of images, contradictory representation. If one person tells me it is white and another that it is black, conflict arises. There is a tendency to judge it black and a tendency to judge it white, and the two tendencies arrest each other. There is consequently a block in the flow of mental activity, so far as it depends on the formation of a judgment on the point raised. Strictly speaking, conflict arises only between alternative continuations of the same mental process. The judgments 'this crow is black' and 'this crow is white' have a common starting-point and divergent continuation. It is divergent continuation from the same point which constitutes the conflict. Conflict arises only between connected processes -- between processes which claim to occupy in some degree the same position in a system of relations. The ultimate explanation of conflict rests, therefore, in the ultimate theory of mental system as such. Theories which locate conflict in the direct incompatibility of mental images would, however, deny this. Yet, except in cases of directly antagonistic processes, such as black-no-black, round-not-round, there would seem to be no intrinsic reason that such conflicts should take place. Theories which find the ground of conflict in the rival claims of different elements in the same system are as varied as the theories of mental SYSTEM (q.v.). Motor theories, however, have the evident advantage in the fact that channels of coordinated action are fewer than those of incidental stimulation; the conflict of the stimulations may thus be due to their rival claim upon the motor channels (cf. Baldwin, Ment. Devel. in the Child and the Race, 286, 308 f., 322 f.; and Münsterberg, Grundzüge der Psychol., i. 534).

Competition, on the contrary, occurs between disconnected processes. It is due merely to the narrowness of consciousness, to the fact that mental activity in a given direction more or less completely excludes activity in other directions. 'The typical instance is what we call distraction of mind, in which attention is solicited simultaneously by a plurality of objects so disconnected in their nature that they cannot be attended to together' (Stout, Analytic Psychol., i. 285).

Both conflict and competition are illustrated in hypnotic somnambulism. The attention is held upon one object to the exclusion of all possible competing objects; and the objects of actual perception in the environment are inhibited by conflict with the suggestions of the hypnotizer. In many instances of the latter case only partial inhibition takes place, and there is a partial adjustment of elements of objective reality with those of the suggested image.

Literature: BINET, L'Inhibition dans les Phénomènes de Conscience, Rev. Philos., Aug., 1890; A. BINET and V. HENRI, Les Actions d'Arrêt dans les Phénomènes de la Parole, Rev. Philos., Jan., 1894; EXNER, Entwurf z. ein. physiol. Erklärung d. psychischen Erscheinungen (1894); BALDWIN, loc. cit.; STOUT, loc. cit.; ODDI, L'Inibizione (1898); COLOZZA, Del potere di inibizione (1898); citations under ATTENTION, and in BIBLIOG. G, 2, d. See also the following topic. (G.F.S.- J.M.B.)

Inhibition (nervous): Ger. Hemmung, Inhibition; Fr. arrêt, inhibition; Ital. inibizione, arresto. Interference with the normal result of a nervous excitement by an opposing force.

It differs from paralysis, in case of which the nervous action is prevented, while in case of inhibition it is overcome, diverted, or neutralized. The normal effect of a higher upon a lower centre of a series is the partial inhibition of the lower. Reflexes may be inhibited voluntarily or by the strong stimulation of sensory nerves up to a certain point.

The conception of inhibition is due to Brown-Séquard. Setschenow attempted to demonstrate a special centre for inhibition (Ueber den Hemmungsmechanismus f. d. Reflexthätigkeit im Gehirn des Frosches, 1863), but it is now conceded that inhibition is a general peculiarity of the interference of nervous activities, which tend to modify each other either by augmenting or repressing (inhibiting) each other. Physiologically, inhibition is a necessary condition in preserving the balance and tone of bodily function. The ganglion cells of the heart, for example, are constantly inhibited by the vagus nerve, and similar control is exercised over all other vital processes. As James says, 'we should all be cataleptics and never stop a muscular contraction once begun, were it not that other processes simultaneously going on inhibit the contraction. Inhibition is therefore not an occasional accident; it is an essential and unremitting element in our cerebral life.' The exact nature of the process remains obscure. Cf. SUMMATION.

Literature: BOMBARDA, Les neurones, l'hypnose et l'inhibition, Rev. Neurol., No. 11 (1897); BROWN-SÉQUARD, Faits nouveaux relatifs à la mise au jeu ou à l'arrêt (inhibition) des propriétés motrices ou sensitives de diverses parties du centre cérébro-rachidien, Arch. de Physiol., 2^e sér. vi (1879); Recherches expérimentales et cliniques sur l'inhibition et la dynamogénie, application des connaissances fournies par ces recherches aux phénomènes principaux de l'hypnotisme, de l'extase et du transfert, Gaz. hebd. de Méd., 2^e sér. xix (1882); Inhibition de certaines puissances réflexes du buble rachidien et de la moelle épinière, sous l'influence d'irritations de diverses parties de l'encéphale, C. R. Soc. de Biol. (1884); EULENBURG and LANDOIS, Die Hemmungsneurose, ein Beitrag zur Nervenpathologie, Wien. med. Wochensch. (1866); JAMES, The Reflex Inhibitory Centre Theory, Brain (1881-2); LANGENDORF, Ueber Reflexhemmung, Arch. f. Anat. u. Physiol. (1877); LISTER, Preliminary Account of an Inquiry into the Functions of the Visceral Nerves, with special reference to the so-called Inhibitory System, Trans. Roy. Soc. (London, 1858); LOEB, Einleitung in die vergleichende Gehirnphysiol. u. vergleichende Physiol. (Leipzig, 1899); McKENDRICK, On the Inhibitory or Restraining Action which the Encephalon exerts on the Reflex Centres of the Spinal Cord, Edinburgh Med. J., xix (1873-4); MUNK, Ueber Erregung und Hemmung, Arch. f. Physiol. (1881); NOTHNAGEL, Beobachtungen über Reflexhemmung, Arch. f. Psychiat., vi (1875-6); ODDI, L'inibizione dal punto di vista fisio-patologico, psicologico e sociale (Turin, 1898); PAL, Ueber Hemmungscentren im Rückenmark, Wien. klin. Wochensch. (1895); SETSCHENOW, Physiol. Stud. ü. Hemmungsmechanismen f. die Reflexthätigkeit des Rückenmarks (Berlin, 1863); SETSCHENOW and PASCHUTIN, Neue Versuche am Hirn u. Rückenmark des Frosches (Berlin, 1865); STEINACH, Ueber die viscero-motorischen Functionen der Hinterwurzeln und über die tonische Hemmungswirkung der Medulla oblongata auf den Darm des Frosches, Pflüger's Arch., 1xxi (1898); VERWORN, Erregung und Lähmung, Verh. d. Ges. deutsch. Naturf. u. Aerzte zu Frankfurt, 1. Theil (1896); also Deutsch. med. Wochensch., xxii (1896); WUNDT, Grundzüge d. physiol. Psychol. (Leipzig, 1893, 4th ed.); see also the other textbooks of physiological psychology and psychology; BREESE, On Inhibition, Psychol. Rev., Monog. Suppl., No. 11 (1899); DANILEWSKY, Ueber die tonischen Reflexe und ihre Hemmung, Arch. f. d. ges. Physiol., 1xxviii (1899); HEYMANS, Untersuchungen über psychische Hemmung, Zeitsch. f. Psychol., xxi (1899); MELTZER, Inhibition, N. Y. Med. J., lxix (1899); PEAVY, Inhibitory Action of the Cerebrum, J. of Amer. Med. Assoc., xxxiii (1899); B. ONUF, A Tentative Explanation of some of the Phenomena of Inhibition on a Histo-physiological Basis, including a Hypothesis concerning the Function of the Pyramidal Tracts, N. Y. State Hosp. Bull. (1897), ii; L. HOFBAUER, Ueber Interferenz zwischen verschledenen Impulsen im Centralnervensystem, Arch. f. d. ges. Physiol., 1xviii (1897); M. HEIDENHAIN, Neue Erläuterungen zum Spannungsgesetz der centrirten Systeme, Morphol. Arb. (Schwalbe), (1897), vii; LOURIE, Riv. di Filos. Scient. (1887-8). (H.P.)

Initiation [Lat. initio, from in + ire, to go]: Ger. Anfang, Initiative; Fr. initiation; Ital. iniziazione. A general term for the starting of a relatively new series of changes.

The term is mostly used in discussions: (1) as to whether the mind, simply by its own act, can initiate changes in its motives or functions generally (the theory of indeterminism: see FREEDOM, and WILL); (2) as to whether consciousness and initiate changes in the brain (see MIND AND BODY); and (3) as to the causes from which spring relatively new movements in history. (J.M.B.- G.F.S.)

Injustice: see JUSTICE.

Innate (in biology) [Lat. in + natus, born]. Ger. eingeboren; Fr. inné; Ital. innato, ingenito. Equivalent to congenital. See ACQUIRED AND CONGENITAL CHARACTERS. (J.M.B.)

Innate Ideas, &c. (in philosophy): Ger. angeborene (Ideen); Fr. (idées) innées; Ital. (idee) innate. Belonging to some sense to the individual himself.

The distinction between ideas which are 'innate' and those which are 'acquired' is an old one in the history of thought. It came to full expression in Descartes, who laid down certain characteristics of innate ideas by which their certainty and value were attested. Locke gave the matter further statement by arguing that there were no innate ideas as such -- meaning notions or actual thoughts inborn with the individual. Kant gave a further turn to the discussion, showing that there were -- as he thought -- certain forms or categories of thought in which all the material of experience was cast and organized in a system of knowledge. To him these forms were universal principles of mental action which could not themselves arise from experience, and which consequently were to be considered innate. In connection with each of these phases of theory the 'acquired' ideas were those items or elements of knowledge which did come through the experience of the individual. The verbal antithesis between the actual words 'innate' and 'acquired' came into use with the Scottish philosophers, who inquired, in a more psychological way, and in detail, into the actual conditions of the rise in the mind of such ideas as cause, space, time, &c.

In current discussion the controversy over innate ideas has taken on a more psychological phase in two directions. First, the question has been removed largely from the sphere of the individual's knowledge to that of the origin of the categories of thought in the race as a whole, called universal. Spencer opened the question, maintaining that although experience might be inadequate to generate these ideas in the individual -- that is, although certain principles of knowledge may seem to be innate to the individual - still they have been acquired by mankind in human evolution through a larger and continuous race experience. Second, the question -- like so many others in the remoulding of the traditional psychology -- has taken on what has been called the 'functional' phase. It is not now claimed by any one that the child is born with a stock of actual ideas, complete and adequate -- the view which Locke combated; on the contrary, it is now asked whether the child comes to his experience with a readiness for certain mental functions, certain characteristic ways of mental action; if so, then these tendencies, of a functional sort, are innate or native, and his experience requires his actual use of such native tendencies. In other words, the mind is not a tabula rasa -- a blank tablet -- as Locke supposed, upon which his experience is gradually inscribed; but experience serves to stimulate the functions and processes which, as a being with a mind, he is constituted to exercise. The insufficiency of the term innate for this new conception has led to its disuse; the terms native and nativism, with modifying words, being now widely current. For further historical matter and literary references see INTUITIONALISM, and NATIVISM AND EMPIRICISM. Innateness is used broadly to cover all the forms of what is innate or native. (J.M.B.)

Innateness: see INNATE (in philosophy), ad fin.

Inner and Outer: see INTERNAL EXPERIENCE, and EXTERNAL OBJECTS; cf. OUTNESS.

Inner Imitation: see SEMBLANCE.

Innervation (sensation of) [Lat. in + nervus, nerve]: Ger. Innervationsempfindung; Fr. sensation d'innervation; Ital. senso di innervazione. A mode of consciousness having the characteristics of actual sensation, supposed to accompany discharge from the central nervous system into the motor apparatus, and to vary in intensity with the intensity of the out-going current. See EFFORT (bodily), and KINAESTHETIC (sensations and equivalents). (G.F.S.- J.M.B.)

The existence of such a sensation in experiences of effort was maintained by certain psychologists (e.g. Biran, Carpenter, Helmholtz) previously to the analysis of the articular, tendinous, and muscular sensation complexes which are called kinaesthetic. An innervation sensation of this kind is still accepted by Bain, Waller, Ladd, Mach, &c.; and Wundt maintained it in his earlier books (e.g. Physiol. Psychol., 1. Aufl.). (E.B.T.- J.M.B.)

Literature: SANFORD, Course in Exper. Psychol., expts. 36-8; BERTRAND, La Psychol. de l'Effort, 96 ff.; CARPENTER, Ment. Physiol. (6th ed.), 388; HELMHOLTZ, Physiol. Optik (2nd ed.), 742 ff.; MACH, Analyse d. Empfind., 57 ff.; WUNDT, Physiol. Psychol. (1st ed.), 316, 488; cf. 3rd ed., i. 404; 4th ed., i. 431, and later books; BAIN, Senses and Intellect (3rd ed.), 77 ff.; LADD, Psychol., Descrip. and Explan., 221; WALLER, Brain (1891), 189 ff.; JAMES, Princ. of Psychol., ii. 493 ff.; DELABARRE, Bewegungsempfindungen (1891); STUMPF, Tonpsychologie, i. 166, 426, ii. 306, 550; also citations under EFFORT (bodily). (E.B.T.- J.M.B.)

Innocence (in law): see IGNORANCE, and INTENTION.

Inorganic: see ORGANIC (1).

Inquisition [Lat. inquisitio]: Ger. Inquisition, Glaubensgericht; Fr. Inquisition; Ital. Inquisizione. An ecclesiastical court of the Roman Catholic Church, called officially the Holy Office, and instituted for the suppression of heresy and certain other offences against morality and canon law.

The Inquisition was formally organized toward the close of the 12th and the beginning of the 13th centuries under Popes Innocent III and Gregory VII, and the principal theatre of its operations included France, Spain, Italy, Portugal, and Germany. It was reorganized in Spain in the 15th century on an ecclesiastico-political basis, and became noted for the severity of its proceedings, especially in connection with the Netherlands. The Inquisition reached its height in the 16th century. It was suppressed in France in 1772, in Portugal under John VI, and in Spain in 1834.

Literature: LEA, Hist. of the Inquisition of the Middle Ages (1887-8); GANS, Kirchengesch. Spaniens (1862-79), iii. 1-93; C. DONAIS, Les Sources de l'Histoire de l'Inquisition, &c., in Rev. des Quest. Hist., xxx (1881); RANKE, The Popes; HEFELE, Cardinal Ximenes (Eng. trans., 1860). (A.T.O.)

Insanity (and Sanity) [Lat. insanitas, from in + sanus, sound]: Ger. Wahnsinn; Fr. démence, folie (mania); Ital. pazzia, follia (pop.), infermità mentale (in law). A serious departure from the normal in the sphere of thought, emotion, or rational action, by way of defect or irregularity. (J.J.- J.M.B.)

The conventional use of the term implies that the disorder is not merely temporary or incidental to a temporary physical condition (a person in a fit of anger, or under the influence of an intoxicant, or in the delirium of fever is not considered insane); while a more special usage eliminates as well the conditions of primary defect (idiocy) and of simple loss or decay of faculty (dementia), and thus confines the term to perversions or aberrant forms of mental functioning (Verrücktheit) which constitute in many cases the salient characteristics of the insane state. There is, too, the legal or practical conception of insanity, which proposes such tests as the ability to distinguish between right and wrong, the being 'of sound mind, memory, and understanding,' the capacity to conduct one's affairs. However necessary and admittedly useful the popular, the legal, and the clinical conceptions of insanity may be, they do not contribute to a clearer understanding of the nature of the defects to which they refer. In distinction from them are the psychological and the pathological or somatic modes of viewing insanity, both founded upon scientific principles, but both also lamentably incomplete; the former considers, mainly, abnormal forms of mental function; the latter diseased conditions of the brain looked upon as the substratum of such function. Both consider insanity not in the restricted or conventional sense, but comprehensively, as the totality of abnormal mental and cerebral conditions. The terms mental pathology and psycho-pathology are better suited to describe what is thus considered than insanity.

Psychology. The factors of greatest importance in the determination of psycho-neuroses (or less accurately the insanities) are precisely those that most profoundly influence normal mental life. Such are heredity and the conditions of existence; inherited natural capacities, and environmental nurtural experiences. Again, mental functions as thus determined are psychologically different, particularly as they involve what are commonly characterized as intellectual, moral, or volitional elements. The various insanities are thus distinguished from one another by their inherited or acquired character, by their special relations to periods of growth or decay, by the symptoms which characterize them, by their relation to known conditions of the nervous system. All of these factors may, and several of them frequently do, combine to the production of a given form of insanity; so that its distinctive name or characteristic may vary according as one or another factor becomes especially prominent. The factors thus enumerated may be spoken of as (1) aetiological, the general causes and conditions of insanity; (2) symptomatic, the mental and bodily abnormal phenomena; and (3) somatic or pathological in the narrow sense, the specific dependence upon diseased conditions of the nervous system. Of these the symptoms are for the psychologist, and probably also for the psychiatrist, the most instructive.

The insanities are also profitably viewed as exaggerations of normal tendencies; and this both generally as abnormalities in the aggregate mental endowment, but still more, specifically, in the distribution and balance of faculties. Insanity is lack of poise and balance more frequently than it is defect or degeneration. Fluctuations in emotional susceptibility, in intellectual power, in practical energy, are normal and psychological, but when these fluctuations exceed normal limits there is insanity; and between there is a wide and vaguely determined borderland. In other words, while despondency and excitement are in themselves normal occurrences, the temperament that gives way upon slight or ordinary occasions to violent fits of dejection, or is prone to periods of exaggerated and wild excitement, is closely akin to that of the victim of melancholia or of mania; while the borderland of eccentricity, of high endowment in a limited sphere combined with marked deficiency in other directions, readily yields illustrations of many typical forms of mental irregularities.

While it may be maintained (Mercier, Morselli) that insanity, like mental processes in general, is to be judged by conduct, this should not be construed to disparage the source of information to be derived from the patient's own description of his feelings and thoughts. It is false to judge insanity, as it is to judge normal action, wholly from without. Perverse motives may lead to wise conduct; a sound decision may be provoked by absurd deliberations and doubts; abnormal tendencies may be resisted and concealed. The very inconsistency between inner feelings and outer conditions often constitutes the psycho-neurosis. It is equally true that an action must be judged in the light of its environment. The ecstatic expression of joy by a child might be a symptom of insanity if manifested by an adult; an action normal for one temperament or in one grade of social life might be so foreign to another as to suggest a mental disorder; the belief in witches and zeal in the persecution of them which was held laudable a few centuries ago might well be regarded to-day as the product of insanity.

Finally, it is well to emphasize again that insanity must not be too exclusively viewed as an intellectual disorder. Perverted thinking, the entertainment of delusions, eccentricities of conduct naturally attract attention; but an abnormality in the emotional sphere, an insensibility to the ordinary motives of action, a personal uncleanliness and indecency which is born of deep alteration of personal and social feelings, a waywardness of action, are far more common than the more picturesque intellectual irregularities, and often determine the latter. In this field, too, lies the basis of the social unfitness of the insane.

Aetiology. The causes of insanity are profitably considered as predisposing and exciting; the former refer to the general concomitant conditions affecting insanity, the latter to the particular occasions and accidents likely to bring it on. Of the former a most prominent factor is the social environment. Insanity has been termed a disease of civilization; its rareness among savages has been noted; its increase in cities and populations most markedly characteristic of modern life has been claimed. It is certainly true that social relations and obligations constitute a preponderant factor in the mental life of sane and insane alike; it is true that the maladaptation and imperfect adaptation of certain portions of all civilized communities is a factor in the production of insanity. But it can hardly be inferred that civilized life, properly developed, in itself predisposes to insanity, however readily it may be admitted that a more complex mental structure with more delicate parts and nicer construction is more liable to faults of mechanism and varieties of derangement than the simpler and more vacant minds of primitive peoples. As between the different strata of society, there seems to be evidence that most of all the very poor -- those upon whom lack of proper nutrition, proneness to alcoholic indulgence, unsuitable hygiene and moral surroundings have worked most severely -- contribute most to the aggregate of insanity; and that again those in easy circumstances, with too little or irrational occupation, prone to much self-indulgence, and over-attention to personal longings and sensations, yield a considerable percentage of the insane. Regarding excessive strain or overwork, the preponderance of opinion seems to indicate that as a factor of insanity this has been highly overrated. It is not work and occupation, but the worry and anxiety accompanying many of the forms of earning a livelihood, the ambition and the strain that incites to unhealthy forms and habits of activity, that should be enumerated as more important aetiological factors of insanity.

Next to the social, the hereditary factors demand notice. One-fourth, or one-third, or even a greater proportion of all regularly enumerated cases of insanity appear in individuals whose families present other cases of insanity or nervous taint. Insanity is graved in the nervous structure. This should not be taken to mean that the insanity, least of all the particular form of it, is handed down from generation to generation; on the contrary, the frequency with which certain members of a family escape the taint which passes on to others in direct or collateral descent, the variety of forms which the taint assumes -- mania here, epilepsy there, neurasthenia or hysteria in a third case, marked but eccentric ability in a fourth -- are most characteristic. What is inherited is properly spoken of as a diathesis (and as such enumerated as a separate aetiological factor), an instability of organization which at certain critical periods of life, or as a result of stress, exhibits the characteristic degeneration. Age is an important factor, especially in relation to the special forms of insanity. Apart from idiocy and imbecility, insanity in the first fifteen years of life is rare; between fifteen and twenty attacks increase, while the two most predisposing decades are those between twenty and thirty, and between thirty and forty, the former perhaps predominating. The period of maturity and fullest expansion of brain power is the danger period of derangement. For different periods different insanities are characteristic: idiocy, spasms, convulsions, epilepsy in the earliest periods; paroxysmal mania, hysteria, great motor and emotional rather than intellectual disturbance in early manhood and womanhood; active mania and delusions in the prime of life, and later melancholia, with dementia in old age. Statistics regarding sex must be interpreted with regard to the proportion of men and women in the general population and the relative low mortality of women; when that is done it is probable that an excess of insanity among males will appear, although this becomes significant only when the special liability of men to certain mental diseases and of women to others is taken into account. (See MANIA, MELANCHOLIA, HYSTERIA, and PARALYSIS.) The effect of consanguineous marriages in the production of insanity is frequently asserted, but it is difficult to determine how far such a factor exists apart from the concentration thus possible of a neurotic diathesis.

Of more specific factors (most of which may be termed exciting) may be mentioned disease of the mother during pregnancy, injury in parturition, accidental injury in later years, intemperance, sexual excess, the stress occasioned by the crises of life, and an endless series of mental, and particularly emotional, shocks or strains. Such exciting causes usually co-operate with the predisposing causes in the production of a specific abnormal state. This is best illustrated in connection with the periods of adolescence, child-birth, the climacteric, &c., at which times latent tendencies to mental break-down become manifest. Such influences have been well discussed by Mercier, under the headings of direct and indirect stress, and again as stress of internal and external origin. The special aetiology of the several forms of insanity has been carefully studied, especially in regard to the exciting causes; these are mainly of interest to the clinical alienist. For a brief tabulation of them see Shaw, as cited below, 137-45.

Varieties of Insanity. An almost endless number of varieties of insanity has been described, particularly by clinical alienists. In the article on Insanity in Tuke's Dictionary of Psychological Medicine some one hundred and thirty varieties are enumerated without exhausting the terms current in medical literature. The classification of these insanities is a vexed question which requires only slight notice in the present connection. A classification is valuable only with reference to the purpose for which it is to be used. The purposes of clinical diagnosis are quite different from those of psychological analysis. The purely practical classifications have attempted to select the salient characteristics of actual cases of insanity, and to group about them as main types subordinates varieties which deviate more or less from them. The result is logically indefensible, but practically useful. Thus Clouston's clinical classification includes, among others, general paralysis, traumatic insanity, alcoholic insanity, phthisical insanity, senile insanity (for details see his work); while his symptomatological classification groups the various forms of defect about states of (1) mental depression, (2) mental exaltation, (3) mental alternation, (4) fixed and limited delusion, (5) mental enfeeblement, (6) mental stupor, (7) defective inhibition, (8) insane diathesis -- all of them variations of psychological functions. But in actual description such terms are supplemented by characteristic groups of symptoms, such as epilepsy, hysteria, general paralysis, &c. In addition to the clinical, the symptomatological, and the psychological classifications, there are those that consider mainly the pathological cause; those that consider mainly the time of appearance, or specific exciting cause; those that consider the association with specific bodily diseases. The psychologist will find most interest in the symptoms of insanity, but cannot afford to neglect the natural groups of which these symptoms are characteristic; while the specific study of the derangements of mental processes in insanity falls under ABNORMAL PSYCHOLOGY (q.v.). For examples of classification consult Shaw, as cited below.

Insanity and the Brain. That normal and abnormal functions alike depend upon cerebral conditions follows necessarily from the modern conception of their nature. But the imperfect state of knowledge regarding the nervous concomitants of mental processes renders it desirable (in this connection) to indicate only a few general and typical correlations. In general abnormal appearances are strikingly frequent in insanity; some of them are local and specific, others general and in part secondary in character. They may be considered as macroscopic and microscopic; as related to insanity in general or to the specific form of it which is present; as related to gross defect or derangement, or to the abnormal symptoms manifested. Thus an abnormally large or small or misshapen cranium, an adherent dura mater, opacity of the arachnoid, arachnoid cysts, hyperaemia or congestion or anaemia or inflammation of the pia mater, atrophy of the cerebral substance, smallness of brain, hydrocephalus, softening of the brain, &c., are some of the pathological appearances frequently met with. More specifically, severe mental defect is generally associated with marked and coarse brain lesions. Thus in idiocy and dementia and epilepsy, abnormality of size and weight of brain, tumours, softening, atrophy, &c., are common, while in mania and melancholia there is frequently nothing to be observed except hyperaemia and slightly uncertain microscopic irregularities. (For the discussion of the special pathology of such conditions see references cited under MANIA, MELANCHOLIA, IDIOCY, and EPILEPSY.) In regard to symptoms the results of localization of function have received corroboration in the field of insanity. Disorders of sight and hearing, of tactile and motor sensibility, paralyses and spasms, motor and sensory speech defects, have been more or less completely correlated with lesions or irritations in definite portions of the brain cortex. EPILEPSY (q.v.) and aphasia (see SPEECH, defects of) best illustrate the extent to which such LOCALIZATION (q.v., cerebral) has been carried. Furthermore, in a great majority of instances we have reason to suspect cerebral changes, which, however, elude any attempt to locate them accurately (cf. Shaw, cited below, chap. vii). See PSYCHOSIS.

Literature: most psychological in treatment are: MERCIER, Sanity and Insan. (1890); HYSLOP, Ment. Physiol. (1895); EMMINGHAUS, Allg. Psycho-Pathol. (1878); MAUDSLEY, Pathol. of Mind (1895); E. MORSELLI, Semej. malat. ment. (3rd ed., 1899); SOMMER, Lehrb. d. psycho-pathologischen Untersuchungsmethoden (1899). For general data of Insanity see KRAEPELIN, Psychiatrie (6th ed., 1899); SPITZKA, Manual of Insan. (1893); KAHLBAUM, Gruppirung d. Psychosen (1863); ZIEHEN, Psychiatrie (1894); FORBES WINSLOW, Aids to Psychol. Med. (1882); KRAFFT-EBING, Lehrb. d. Psychiat. (1879); ADAMKIEWICZ, Functionsstörungen d. Grosshirnrindes (1898); CLOUSTON, Ment. Diseases (1887; 5th ed., 1898); BUCKNILL and TUKE, Manual of Psychol. Med.; SAVAGE, Insanity (1884 and 1896); CHURCH and PETERSON, Nerv. and Ment. Diseases (1898); BEVAN-LEWIS, Ment. Diseases (2nd ed.); MEYNERT, Klin. Vorlesungen ü. Psychiatrie (1890); SÉGLAS, Leçons cliniques sur les Malades mentales (1887-94); G. BALLET, Les Psychoses (Ital. trans. by MORSELLI with additions, 1895). Many of the systems of diseases contain excellent contributions on mental diseases, particularly Ziemseen's Cyc. of the Pract. of Med., The Twentieth Cent. Pract. of Med., &c. J. SHAW, Epitome of Mental Diseases (1892), is a convenient reference book. (J.J.)

Insanity (in law). Such lack of mental soundness as makes one who does a particular act incapable of appreciating its real character.

Law deals in all instances with particular acts, and (except with reference to putting an alleged lunatic under guardianship) the question of sanity or insanity is to be determined in each instance with reference to the act in question. Monomania does not destroy testamentary capacity, unless it touches something involved in the particular will. So, though one has been put under guardianship as a lunatic, this action does not necessarily deprive him of the ability to make a will or to commit an actionable wrong or crime.

Literature: see chapter on Insanity in its Medico-legal Bearings, in HAMILTON, Syst. of Legal Med., ii. 19. (S.E.B.)

Insects [Lat. in + secare, to cut]: Ger. Insekten; Fr. insectes; Ital. insetti. The insects, or Hexapoda, form a class of the phylum Arthropoda, in which the body is divided into three regions; head, thorax, and abdomen.

There are typically a pair of sensory antennae, eyes, a pair of mandibles, and two pairs of maxillae on the head; three pairs of legs and two pairs of wings on the thorax. The ventral genital pore is situated near the extremity of the abdomen. The Hexapoda are typically air-breathing and tracheate animals, of terrestrial or aërial habit in the adult state; they are remarkable for the perfection of their sense-organs, and the high development of their instincts and ability to perform acts which seem intelligent. This is especially true of those which form social communities.

Literature: J. LUBBOCK, Origin and Metamorphoses of Insects (1874); Ants, Bees, and Wasps, Int. Sci. Ser. (1882); and On the Senses of Animals, Int. Sci. Ser. (1888); D. SHARP, Insects, in the Cambridge Nat. Hist., Pt. I (1895), Pt. II (1899); A. S. PACKARD, Textbook of Entomol. (1898); W. KIRBY and W. SPENCE, Introd. to Entomol. (1816-28); G. W. and E. G. PECKMAN, The Instincts and Habits of the Solitary Wasps, Wisc. Geol. Survey Bull., No. 2, 1898 (valuable). Cf. COMPARATIVE PSYCHOLOGY, and INSTINCT; and see BIBLIOG. G, 1, f. (E.S.G.)

Insensibility: see ANESTHESIA.

Insight [in + sight]: Ger. Einsicht, Anschauung; Fr. connaissance profonde (no exact equivalent); Ital. intuizione. (1) Apprehension of the more subtle and profound aspects of truth in a relatively immediate and direct way.

(2) The organ of higher intuition or reason, held to afford direct contemplation of truth.

The use of the term varies from the more refined and penetrating processes of thought to the supposed faculty of CONTEMPLATION (q.v.) of the mystics. (J.M.B.)

Insistent Idea: see IMPERATIVE IDEA.

Insolubilia [Lat. in + solvere, to loose; trans. of Aristotle's aporia; used mainly in plural]. A class of sophisms in which a question is put of such a nature that, whether it be answered affirmatively or negatively, an argument unimpeachable in form will prove the answer to be false.

The type is this: Given the following proposition:

This assertion is not true: is that assertion, which proclaims its own falsity, and nothing else, true or false? Suppose it true. Then,
Whatever is asserted in it is true, But that it is not true is asserted in it; Therefore, by Barbara, That it is not true is true; Therefore, It is not true. Besides, if it is true, that it is true is true. Hence, That it is not true is not true, But that it is not true is asserted in the proposition; Therefore, By Darapti, Something asserted in the proposition is not true; Therefore, the proposition is not true. On the other hand, suppose it is not true. In that case, That it is not true is true, But all that the proposition asserts is that it is not true; Therefore, By Barbara, All that the proposition asserts is true; Therefore, The proposition is true.

Besides, in this case, Something the proposition asserts is not true, But all that the proposition asserts is that it is not true; Therefore, By Bokardo, That it is not true is not altogether true; Therefore, That it is true is true; Therefore, it is true.

Thus, whether it be true or not, it is both true and not. Now, it must be either true or not, hence it is both true and not, which is absurd.

Only two essentially distinct methods of solution have been proposed. One, which is supported by Ockham (Summa totius logices, 3rd div. of 3rd part, cap. 38 and 45), admits the validity of the argumentation and its consequence, which is that there can be no such proposition, and attempts to show by other arguments that no proposition can assert anything of itself. Many logical writers follow Ockham in the first part of his solution, but fails to see the need of the second part. The other method of solution, supported by Paulus Venetus (Sophismata Aurea, sophisma 50), diametrically denies the principle of the former solution, and undertakes to show that every proposition virtually asserts its own truth. This method, therefore, denies the premise of the antithesis that 'all that the proposition asserts is that it is not true,' since, like every other proposition, it also asserts its own truth, and is therefore contradictory and false, not in what it expressly asserts, but in what it implicitly asserts. Some writers (as Fries) hold that because every proposition asserts its own truth, therefore nothing is a proposition which asserts its own falsity. See Aristotle, Sophisticae Elenchi, cap. 25. Other proposed solutions of little importance are given by Paulus Ventus, loc. cit. (C.S.P.)

Insomnia [Lat. in + sommus, sleep]: Ger. Schlaflosigkeit; Fr. insomnie; Ital. insonnio. Sleeplessness, inability to sleep.

The amount of normal sleep varies with the period of life and the individual; any marked deficiency in habitual sleep might be termed insomnia, although the term is usually restricted to a more or less chronic defect due to some disturbance of the nervous system. Defective sleep may consist of a deficiency in quality as well as in quantity, although insomnia refers usually to the latter alone. The two frequently exist together. The causes of the insomnias are various; some are due to bodily disorders, but most are of nervous origin. It is common among the insane, and is often the most distressing accompaniment of melancholia. In weakened conditions of the nervous system in those temperamentally disposed to nervous disorders, insomnia is apt to be caused by slighter degrees of the same influences -- such as worry, grief, excitement -- that produce it in others.

For artificially produced loss of sleep see SLEEP.

Partial sleeplessness may lead to SOMNAMBULISM (q.v.) and AUTOMATIC ACTION (q.v.). The medical literature is concerned with the treatment of insomnia; and for this purpose PSYCHO-THERAPEUTICS (q.v.) have been tried with considerable success.

Literature: H. M. LYMAN, Insomnia (1885); MACFARLAND, Insomnia (1890); C. EDGELOW, Modern Sleeplessness (1891); E. YUNG, Le Sommeil normal et le Sommeil pathologique (1893); BROWN, Disorders of Sleep, in Twentieth Cent. Pract. of Med., x. 813. (J.J.)

Inspiration [Lat. inspiratio, from inspirare, to breathe into]: Ger. Eingebung; Fr. inspiration; Ital. ispirazione. (1) An illumination or simulation of the human mind which is conceived to be of supernatural origin.

(2) The doctrine that the writers of the Christian Scriptures were so informed and guided by the Holy Spirit as to make them truly express the mind and produce the word of God.

In the first sense Socrates was inspired by the suggestion of his daimon. So also the divine illumination of Philo and the intuition of the mystics are inspiration in the first sense. In the narrower and more technical sense of the term it is distinguished by exact writers from Revelation, which means original communication of truth, and is confined to the process of its transmission. Theories of inspiration have been various, as for example (1) verbal, the dictation of the words of the message by the Holy Spirit; (2) plenary, that the Scripture is fully inspired in all its parts; (3) limited or partial, that only parts of the Scripture are fully inspired or that only certain elements are inspired.

Literature: DELITZSCH, De Inspiratione Scripturae Sacrae (Leipzig, 1872); ROHNERT, Die Inspiration d. heiligen Schrift (Leipzig, 1889); RABAUD, Hist. de la Doctrine de l'Inspiration (Paris, 1883); JOHN DE WITT, What is Inspirational? (N.Y., 1893); WESTCOTT, Introd. to the Study of the Gospels; LADD, Doctrine of Sacred Scriptures (N.Y., 1883). (A.T.O.)

Instability [Lat. in + stabilis, stable, from stare, to stand]: Ger. Unbeständigkeit; Fr. instabilité; Ital. instabilità. Relative liability to DISSOCIATION AND DISAGGREGATION (q.v.), either mental or nervous.

Instability is a general word for all sorts of retrograde or disintegrative tendencies. In psychology it is applied particularly to lack of persistence or effectiveness in the functions which involve synthesis and organization. Cf. Duprat, Instabilité mentale, and the textbooks of mental diseases (in which the term is often used without clear definition). (J.M.B.)

Instinct [Lat. instinctus]: Ger. Instinkt; Fr. instinct; Ital. istinto. (1) An inherited reaction of the sensori-motor type, relatively complex and markedly adaptive in character, and common to a group of individuals.

(2) Native endowment of any kind; the adjective instinctive is frequently used in this sense. This meaning is not recommended; the terms congenital, innate, and impulsive serve this purpose adequately.

(1) This definition makes instinct a definitely biological, not a psychological conception. No adequate psychological definition of instinct is possible, since the psychological state involved is exhausted by the terms sensation (and also perception), Instinct-feeling, and IMPULSE (q.v.). This definition, it will be seen, rules out the application of the term instinct to tendencies and impulses which do not have definite native motor channels of discharge. The line of difficulty with this definition lies in the distinction of instinct from reflex action; but the facts that instinct is definitely associated with stimulation through the higher centres (sensori-motor), and that it is highly adaptive and relatively complex, while reflexes are relatively simple and not always evidently adaptive, serve to differentiate them. On the other hand, the distinction of instinct from action of the secondary-automatic type is in their origin respectively, the former being congenital, the latter acquired. Further, they differ psychologically in that instincts may involve a high degree of consciousness, with attention; and also inasmuch as secondary-automatic acts exhibit the progressive conative determination, described under HABIT (q.v.), as the instincts do not.

The must discussed question of the origin of instincts has given rise to various theories. There are two main views, called respectively the 'lapsed intelligence' and the 'reflex' theory. According to the former, instincts have arisen through intelligent accommodations which have become secondary-automatic actions, and have been transmitted by physical heredity. This theory is held by Wundt, Eimer, Cope, &c. The principal difficulty with it is the lack of evidence of the actual transmission of acquired characters, together with the difficulty of supposing sufficient intelligence so far back in the history of life. The psychological differences between instinct and secondary-automatic actions also create a difficulty (Stout). The other great class of theories -- the reflex theories -- hold that the instincts have arisen by the gradual accumulation of reflex adjustments to the environment; a compounding of such adjustments, which may be both congenital adaptations, or variations, and individually acquired organic accommodations (as think those who hold to the inheritance of acquired characters, e.g. Spencer), or only congenital adaptations (those who do not so hold). The main objections to this theory are that it does not account for the survival of the early beginnings of an instinct before it is of utility, and also that it does not account for the facts of co-ordination of muscular groups. The two views are held by some (Romanes) to be both partly true. A third point of view consists in the application of the principle of ORGANIC SELECTION (q.v.) to some instincts; according to which accommodations of all kinds, whether intelligent or organic, may serve to supplement incomplete endowment and so keep a species alive until variations are secured sufficient to make the instinct relatively independent (L1. Morgan, Baldwin, Groos, Stout). Cf. COINCIDENT VARIATION.

Literature: general works on psychology, and works on COMPARATIVE PSYCHOLOGY (q.v.); also many of the titles given under EVOLUTION, and BIBLIOG. G, 1, f, 2, l. Further: LL. MORGAN, Some Definitions of Instinct (Nat. Sci., May, 1895), Habit and Instinct, and Animal Behaviour (1900); GROOS, The Play of Animals, and the Play of Man (Eng. trans.); ROMANES, Ment. Evolution in Animals (especially the Appendix, a posthumous paper by CHARLES DARWIN), and Darwin and after Darwin, Pt. I; BALDWIN, Science, March 20 and April 10, 1896, and Story of the Mind, chap. iii; LICATA, Fisiologia dell' istinto (1879); MASCI, Teorie sulla formazione naturale dell' istinto, R. Accad. Sci. (Napoli, 1893); WHITMAN, in Woods Holl Biol. Lects. (1899). (J.M.B., G.F.S., C.LL.M.)

Instinct-feeling: see IMPULSE.

Instinctive Morality: Ger. instinktive Moralität; Fr. moralité instinctive; Ital. moralità istintiva. (1) Conduct exhibiting the external marks of moral conduct, but due to instinctive action of the individual nature in given circumstances, and not to deliberate choice.

Instinctive morality is thus without knowledge of the nature of morality (of the distinction between good and evil) and accordingly without choice of the good as good.

At the same time it may be the basis upon which conscious morality is built up in the individual character. The facts of instinctive morality are exhibited in the conduct of races and of children before the stage of moral reflection has been reached. Thus the social instinct is held (as by Hutcheson, Inquiry, iii. 15) to be a 'principle of virtue.' (W.R.S.)

(2) The term is also used to indicate a supposed moral instinct by which conduct is regulated without further intellectual or other preparation or cultivation. It is in so far a form of the native or intuitive theory. (J.M.B.)

Institution [Lat. institutio]: Ger. Institution; Fr. institution; Ital. instituzione. Any established and successful arrangement for carrying out a purpose, such as business, education, &c.

Certain of the most important, apart from private establishments, are (1) social institutions -- those belonging to or administered by SOCIETY (q.v.); and (2) political institutions -- those belonging to or administered by the STATE (q.v.). (J.M.B.)

Instruction [Lat. instructio, from in + struere, to build]: Ger. Unterricht; Fr. instruction; Ital. istruzione. The teaching act whereby the pupil is informed and also trained and stimulated to acquire knowledge and mental power. (C.DE.G.- J.M.B.)

It concerns itself chiefly with three things: the materials, the course, and the methods of instruction. The materials of instruction are the literature and science that constitute human knowledge. Its first stage is to enable the pupil to master the symbols that pertain to the acquisition and expression of knowledge; that is, the pupil must first be taught to read, to write, and to compute. He must next be taught the most patent facts that influence his intellectual, moral, and social life. The curriculum of study has varied with the complexity of life and the national ideals of the place and function of the individual. Democratic society demands the open door into every department of human activity, hence the ideal elementary curriculum in a system of universal education furnishes the essential elements of all human culture. It lays the foundations for the mastery of the quantitative sciences by mathematical training, and for the humanities by its instruction in history, literature, grammar, civics, and geography. In the secondary period the curriculum is usually limited to fewer branches, but still to those typical of all culture. It differs chiefly from the elementary course of study by its more intensive character and its more scientific methods.

The course of instruction depends upon the age, ability, and natural interests of the pupils. In the earlier years of school life its course of procedure is governed more by the psychological needs of the pupil than by the logical unfolding of the subject. During the high school period, however, the course of instruction follows much more closely the order of scientific procedure, causal relations being more emphasized than accidental ones. Herbart recommends the blending of three orders of progress, namely, (1) the merely presentative, which gives facts; (2) the analytic, which separates wholes into their elements; and (3) the synthetic, which presents in proper order and relation the manifold material of human culture.

The method of instruction varies with the knowledge and capacity of the pupil. In the early years the steps must be short, the relations of subject-matter simple, the strain upon the attention brief; while the presentation should be varied, vivacious, and interesting. In the high school the methods of instruction follow more closely the analogies of scientific investigation, being for the most part inductive in character and involving the lesser systems of relationship; thus, for example, botany will involve the function of organs as well as the naming and classification of plants; it will involve also a study of the relations of the plant to its environment of earth, air, temperature, and light. See METHOD (educational), ANALYSIS, and SYNTHESIS.

Literature: HERBART, Sci. of Educ. (trans. by Felkin), 135-93; ADAMS, Herbartian Psychol. applied to Educ., 81-187; H. SPENCER, Education; ROSENKRANZ, Philos. of Educ., 106-43; HARRIS, Psychol. Foundations of Educ., 321-400; BAIN, Educ. as a Science, 146-396; BALDWIN, Story of the Mind, chap. iii; DE DOMINICUS, Linee di Pedagogia, 3 vols. (1897); R. ARDIGO, La Scienza dell' Educazione (1893). (C.DE.G.)

Insurance [OF. enseurer, to insure]: Ger. Versicherung; Fr. assurance; Ital. assicurazione. A contract whereby the person insured pays a relatively small sum, in order to receive a larger sum in case of a contingency which would otherwise cause him a loss. The term assurance is also used, especially for other forms than life insurance.

It is the last clause which distinguishes insurance from GAMBLING (q.v.). Insurance contracts and gambling contracts are both wagers, and may be exactly alike in form; but if such a contract is made for contingent gain, it results in loss of utility and in commercial demoralization; while if it is made to prevent contingent loss, it results in increase of utility and in commercial security. See Jevons, Theory of Political Economy. (A.T.H.)

A special theoretical interest attaches to insurance from the fact that it is based upon a statistical treatment of PROBABILITY (q.v.). The unit payment of premium, p, represents -- apart from cost and profits to the insurance company -- a sum which, multiplied by the coefficient a, gives the quantity b, that is

The quantity a is a function of the serial distribution of the annual payments with the subordinate coefficients a', a'', a''', &c. -- the calculated numbers of years' payments of the insured based on (e.g.) vital statistics; that is

The quantity b is the sum of the face values of all the policies issued -- apart from the settling of disputed claims, forfeitures, &c. We accordingly have, disregarding corrections for the fluctuations of b,

p = ______b_______
      a' + a'' + a''' + . . .

giving a value of p which insures the company against loss. The point of interest is that p is a function of the a values, which are calculated probabilities of life in years of persons of different ages. The application of the method, in practice, to all sorts of social and moral facts only awaits the gathering of statistics to furnish data for the preparation of tables like those for mortality. (J.M.B.)