INTROSPECTION. – It is the method of analysis of the appearance and content of psychic processes through self-observation, which is called introspection when it is conducted in a systematic manner and according to precise scientific criteria. In this sense, a distinction is made between auto-introspection and hetero-introspection: in the former, the subject observes and describes the immediate contents of consciousness on his own, while in the latter he does so following the instructions of the experimenter. The foundation of introspection lies in the capacity of spiritual consciousness to reflect upon its inner functions and to consider their objects and acts: «Intellectus supra seipsum reflectitur, secundum eamdem reflectionem intelligit et suum intelligere et speciem qua intelligit» (Sum. Theol., 1 p., q. 85, a. 2). Although knowledge is primarily directed toward the object, it simultaneously perceives its act and the subjective structures of its functions or the species of the Scholastics: «Et sic species intellecta secundario est id quod intelligitur» (ibid.).
The method of introspection was brought to prominence especially by the Denkpsychologie of the Würzburg school (Külpe) and had the merit of overcoming positivism and phenomenism in psychology. The method of introspection was anticipated in criticism by Reid (Essay on the faculties of the human mind, I, 3; ed. Hamilton, vol. II, Edinburgh 1863, pp. 518 ff.) and especially by Kant, according to whom «the inner sense – unlike the outer sense, which can see objects in space at rest and thus observe them at leisure – perceives the relations of its own determinations only in time and therefore in their flux, where that constancy of observation is lacking which, however, is a necessary condition for experimentation» (E. Kant, Anthropologie, part 1, I, § 4: Von dem Beobachten seiner selbst, in Werke, ed. E. Cassirer, VIII, Berlin 1922, p. 18). Similar criticisms of introspection have been advanced by Herbart, Comte, and Höffding. A middle way is suggested by Gestalt psychology, according to which introspection also appears as a field of «structural organization,» which presents it in its contents and functions (cf. K. Koffka, Principles of Gestalt Psychology, London 1936, p. 319), but in doing so it approaches the objective method of «behavior» (behaviorism). In philosophy, the method of introspection has had particular development in the intuition of Bergson and in the phenomenology of Husserl’s school; however, this direction has tended toward an introspection in the transcendental idealist sense of consciousness.