PERCEPTION. – In general, it denotes awareness of something both in external and internal experience and becomes almost synonymous with “consciousness” (v.): p. therefore entails a certain “judgment of existence” object (v.) in the field of consciousness. In a stricter sense, p. may be defined as the complete act of concrete knowledge, insofar as it performs the synthesis of the sensory and intellectual spheres.
In pure sensation there is the presence of the quality (colors, sounds... figures, movements), but through sensation alone (v.) one does not yet possess the real “meaning” of the quality, which is obtained only as a function of the “whole” apprehended by the subject, finding its definitive expression in the “concept” (v.). But even the pure concept, such as man can have it when experience (v.), cannot by itself reach the concrete, multiple, and mutable; consequently, it pronounces only upon the formal value of the contents of experience, without grasping their reality of existence. P. is the synthetic act of consciousness that actualizes and contains both movements in the dynamic unity of sensory and intellectual consciousness. In Thomistic psychology, p. of the existing singular, when it concerns objects of the external world, does not properly belong to the intellect as such, but insofar as the intellect embraces sensibility within the unity of consciousness and continues in particular through the cogitativa (v.), which is man’s proper internal sense, by means of which the intellect performs the “conversio ad phantasmata” and thus its conjunction with existing reality: in this sphere, therefore, p. is immediate, although indirect (“Indirecte et quasi per quandam reflexionem...”: Sum. Theol., 1°, q. 86, a. 1). In spiritual life, on the other hand, man has immediate and direct p. of his own acts and of the acts of his very existence (ibid., q. 87, aa. 1-4); and it must be called immediate and direct even though it is secondary, insofar as it is conditioned by the apprehension of the objects toward which consciousness is directed in the first place. Aristotle speaks of an “accessory” knowledge, ἐν πυρέψῃ (Met., XII, q. 1074, b 36), which St. Thomas clarified by seeking to bring it closer to Augustinian inwardness: “Et ideo id quod primo cognoscitur ab intellectu humano est huiusmodi obiectum, et secundario cognoscitur ipse intellectus cuius est perfectio ipsum intelligere” (Sum. Theol., 1°, q. 87, a. 3).
Modern psychology has oscillated between the elementary theory of p. association of ideas (v.) and the synthetic theory of Kantian derivation, which received an original interpretation in the “theory of form” (Gestaltheorie).