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IDEA. 445 IDENTITY. ciples of Psychology (ib., 1890) ; Titchener, Out- line of Psychology (New York, 1899). IDEALISM. In philosophy, the theory that no reality is independent of consciousness. Its ordinar)- antitliesis is realism, or the theorj' that the reality ot" things is not dependent upon their relation to consciousness. The motif of idealism can best be understood by contrasting idealism with agnosticism or skepticism (q.v. ), which admits the existence or at least the possibility of reality in independence of consciousness, but denies the possibility of knowing such reality. A typical skeptic, such as Hume, admits that we do know the contents of our own consciousness. Most skeptics, among them Hume, go to the ex- tent of formulating laws in accordance with which the.'ie contents appear and vary. But all this knowledge, satisfactory as it is in its own spliere, is knowledge only of phenomena, or of ideas in the Lockean sense of the word. Skep- ticism is thus idealistic in its epistemolog}' or theory of knowledge, while anti-idealistic or non- committal in its ontology (q.v.). The idealist escapes skepticism by refusing to take into con- sideration the possibility of the existence of a non-ideal reality. The realist asserts the exist- ence of the non-ideal reality which the skeptic either admits or doubts without denying, but u-sually the realist also asserts the possibility of knowing that reality. Thus the idealist and the realist are antagonistic, both in epistemology and ontology, while the skeptic sides with the idealist in epistemology and yet refuses to take sides against the realist in ontology. Idealism has taken numerous forms. Among these may be mentioned subjective idealism, which assigns only subordinate reality to the content of consciousness and ultimate reality only to the conscious subject (Berkeley and Fichte) ; objective idealism, which interprets nature as reason made an object to it- self (Schellinp) : absolute idealism, which assigns ultimate reality only to the unity consisting of both object (contents) and consciousness in indissoluble correlation (Hegel) : and transcen- dental idealism, which regards the world of ex- perience as dependent for its order upon the ac- tion of a conscious subject working in accordance with laws of thought, but which at the same time denies that ultimate reality is dependent upon such action (Kant). For a criticism of idealism, see Knowledge, Theory of ; and see also Plato ; Plotinus ; Neo-Platomsm ; Berkeley ; Kant; Fichte: Sciiellixg : Hegel : Lotze; Green, Thomas Hill. Consult: Willmann. Ge- schichtr des Idealism us (Brunswick, 1894-97), and the aithorities referred to under Knowledge, Theory of: Met.aphysics. For the question of idealism in literature, see Rom..ticism ; Realism and Xatcralism. IDEAS, Association of. See Association OF Ideas. IDELER, e'de-ler, Chkisttan Ludwig (1766- 1846). A German astronomer and chronologist, born at Gross-Brese. near Perleberg. in Prussia. After holding various oflBces he received a pro- fessorship at the University of Berlin in 1821, and in 1 S29 he was made a foreign member of the Institute of France. Ideler's most important ■works are: Handbuch der mathematischen und technischen Chronologic (2 vols., 1825-26; 2d ed. 1883), which was the first work that pre- sented a clear view of the reckoning of time among the ancients; and Die Zeitrechnung der Ckinesen (1839), a supplement to the Uandbuch. He also wrote, in conjunction with Xolte, hand- books of the French and English languages and literatures, which passed through numerous edi- tions. IDEN, i'den, Alexander. A Kentish squire in Shakespeare's ^ Henry 17., the slayer of Jack Cade. IDENTITY (ML. identitas, sameness, from identicus, same, from Lat. idem, same) , The Law of. The principle that in any train of thought, such as a syllogi.sm, there must be running through all the diiferences of contents a oneness of meaning, in which is found the consistency of the phrase of thought. This definition leads to the consideration of the dispute about the mean- ing of identity. Some have maintained that it is undilTerentiated sameness, and that the differences which are found among similar things are accre- tions of unlikenesses around the core of sameness. Others have maintained that no two objects of consciousness are exactly alike, and that identity is not undifferentiated likeness, but a likeness in difference or a differentiated likeness. The debate centres around the conception of philosophical atomism. It is possible by abstraction to obtain an idea of some quality which is the element of likeness between several objects, and which can be thought as itself undifferentiated. Take color, for instance. In all the different colors, such as red, green, and yellow, can wc find by abstraction some one element which is undifferentiatedly alike? Suppose we say that it is that quality of the visual .sensation which is due to the stimulus of (relatively) homogeneous light vibrations. (See Color.) Even the answer does not secure undifferentiated likeness. That quality thus pro- duced is not one quality, but it is "at least 160 spectral color qualities" (Titchener). each irredu- cible to any other. But even these are not sharp- ly defined against each other. Although we can- not distinguish all the differences, there is everv* reason to suppose that there are differences which, though they affect our experience, we are not attentively aware of. There is a continuum of color. ( See Continuity. Law of. ) If so, there is no undifferential sameness of color, although there is a sameness which we recognized in the differences. There is a oneness in all the reds, which oneness we cannot isolate, although ice can recognize. So there is a oneness in all color, uni- solable but distinguishable and recognizable. What is true of color is true of everything else. Atomistic explanation of color is false to fact. Undifferentiated sameness is not offered by ex- perience. Hence an identity might be defined as an unisolahle but distinguishable oneness of attri- butes in objects which at the same time might present a multiplicity within the same attributes. For the atomistic views of identity, consult .Tames, Principles of Psychology (Xew York. 1893) ; for the opposite view, Bradley, Principles of Logic. books i., ii. (London. 1883) : also the discussion between .James and Bradley in Mind, new series, vol. ii. (London. 1893) ; Bradley. .ipj>earance and Reality (see index for pertinent passages) (Lon- don. 1897) : Bosanquet. Logic (see index for pertinent passages) (London, 1888) : Fullerton. ffameness and Identity (Philadelphia. 1890) ; also the authorities referred to under Logic; Knowl- edge, Theory of.