SENSISM. — A philosophical sensation (v.) as the sole source of knowledge and resolves thought (v.) into II. S. therefore opposes a substantial distinction between sense and intellect, concept (v.). It differs from sensationalism, which understands reality itself, phenomenistically, as pure sensation, and from sensualism, which in Italian has an exclusively ethical meaning and indicates, hedonism (v.), the system that places the norm of morality in sensible pleasure. Terminology is more uncertain elsewhere: in French, German, and English, sensualism is in fact used with the meaning of s., a term lacking in those languages (recently W. Brugger introduced it [Sensismus] in his Philosophisches Wörterbuch, Vienna 1948).
S. represents, in a certain sense, rationalism (v.); deriving all knowledge from experience, it opposes the various forms of innatism (v.) and logically entails the denial of a theoretical knowledge valid beyond experience itself (positivism [v.]).
The first formulations of s., but with a meaning intended to be merely psychological, are found in pre-Socratic philosophy. Indeed, despite the gnoseological dualism that emphasized the distinction between opinion or empirical-popular knowledge (βῆζα) and truth or rational knowledge (ἀληθε), Parmenides affirms the substantial identity between thought and corporeality (Diels, fr. 16 B, I, p. 244, 8; Aristotle, Met., III, 5, 1009 b 21-25; cf. Gli eleati, edited by P. Albertelli, Bari 1939, p. 155). For Empedocles, “thinking and perceiving are the same thing” (Aristotle, De anima, III, 3, 427 a 19-20; cf. Met., III, 5, 1009 b 12-13), and according to Protagoras, “the soul is nothing apart from sense” (Diogenes Laertius, IX, 51; cf. Plato, Theaet., 152 a, c): Protagoras’s s. constituted the premise of gnoseological relativism, since sense perception, conditioned by the individual subjective-objective moment, has no value of universality. Stoic gnoseology is also sensistic: “Through the senses nature offers us notions of things” (fr. 66: N. Testa, I framm. degli stoici antichi, I, Bari 1932, p. 36; cf. fr. 62, ibid., p. 32): experience, concepts, and science have their sole source in sensation. S. is equally Epicurus (v.): “all rational knowledge proceeds from sensations” (πᾶς λόγος ἀπὸ τῶν ἀλόθηκων ἡρτησαι: Diogenes Laertius, X, 32). In early Christian thought, Tertullian inclined toward s., as did Arnobius, not without the influence of Epicureanism (cf. Adversus Gent., II, 16-20 ff.: PL 5, 833 ff.). Medieval thought, even in the nominalist orientation of the 11th and 14th centuries, maintained the substantial distinction between sense and intellect, and therefore one cannot speak of s. in scholasticism; nevertheless, the principles of s. were latent in Occamism’s devaluation of universal knowledge (v. NOMINALISM; OCCAM). It is equally inaccurate to attribute s. CAMPANELLO (v.): he holds that the universal, as idea and concept, though not as common notion, transcends sense: “homini... mentem divinam immitti, quandoquidem in eo apparent operationes quae non in caeteris” (Prodromus, Frankfurt 1617, p. 85, in G. Di Napoli, T. Campanella, Padua 1947, p. 278 ff.). In modern thought, s. HOBBES, THOMAS (v.): there is no distinction between soul and body, and therefore “all knowledge and science derives from sensation” (cf. Leviathan, I, 1 and 34), understood passively as the movement of the organic subject toward the object; deterministic-mechanical association accounts for all psychic processes. LOCKE, JOHN (v.), although he asserts that every idea derives from experience (Ess., II, 1, § 2), nevertheless goes beyond s., insofar as he recognizes, alongside sensation, “reflection” or the internal perception that the soul has of its own acts as a source of knowledge (ibid., 4 ff.). S. materialism (v.) in Lamettrie: the entire psychic life is a function of the brain, and every content of knowledge derives from the senses and is resolved into sensations. In Lamettrie, Helvétius (v.), sensistic materialism translated, on the ethical plane, into hedonism: there is no motive for moral action other than individual utility and interest, even when pursued through obedience to the laws; to be “moral” is, ultimately, merely a way of being happy. The most characteristic expression of s. in the Condillac (v.). He accepts Lockean empiricism, but resolves the second source of knowledge, “reflection,” into sensation as well: “sensation envelops all the faculties of the soul” (Traité des sens., I, 7, § 2). Every content of knowledge and all its functions are therefore nothing but sensations elaborated and transformed (“sensations transformées”): attention, abstraction, reflection, analysis, synthesis, imagination, comparison, judgment, and syllogism are simple characteristics (vividness, persistence...) or relations (of concomitance, succession, coordination, resemblance, distinction...) of sensations. Similarly, in the affective sphere, all feelings (love, fear, hope, desire, the will of the good...) derive from the fundamental character of pleasure-displeasure inherent in sensations. But, unlike Lamettrie (whose materialism, as Lange demonstrated in Gesch. d. Materialismus, I, part 1, chap. 2; Italian trans. Milan 1932, p. 337 ff., does not derive from Condillacian s.), Condillac gives his s. a spiritualistic orientation: he does not exclude the existence of a spiritual soul, distinct from matter and motion, which is the subject of sensations (cf. De l’art de raisonner, I, 3). Condillac’s s., as an empirical systematization of the genesis and development of knowledge, enjoyed wide success and became, in France, the official philosophy of the second half of the eighteenth century (v. IDEOLOGY); among the “ideologists,” Ch. Bonnet (v.) preserved a spiritualistic character in s. It Romagnosi (v.), Soave (v.), Borrelli (v.). Subsequently, s. accompanied the development of materialism: Robinet; Cabanis (there is no soul distinct from the body; psychic functions are resolved into chemical nervous processes [Diderot had understood them as mechanical processes]: thought as a secretion of the brain); Czobel (consciousness is a pure copy of material reality, and its representations too possess extension; cf. Neue Darstellung d. Sensualismus, Leipzig 1856); Feuerbach (moral s.: morality and action are directed solely by the pursuit of happiness, whose criterion is sensation). S. is also associated with Humean empiricism (v. HUME): the power of the mind and of thought is ultimately nothing but “the faculty of composing, transposing, increasing or diminishing the materials furnished to us by the senses and experience” (Enquiries, sec. II, § 13, ed. Selby-Bigge, repr., Oxford 1932, p. 19); nor does it remain foreign to the postulates neopositivism (v.). In France it was opposed by the spiritualistic orientation of Maine de Biran, Jouffroi, and Cousin.
S. presents a positive insight already advanced by Aristotle against Plato’s innatistic idealism and accepted by Thomism: the objective-functional dependence of the activity of thought upon the forms of sensibility. The principle “nihil est in intellectu quod prius non fuerit in sensu” (cf. St. Thomas, De verit., q. 2, a. 3 ad 19) can have a correct meaning, insofar as no object becomes actual in thought without an immediate or mediated relation to the data of sensible knowledge: “sine sensu non potest aliquis homo addiscere, quasi de novo acquirens
scientiam, neque intelligere, quasi utens scientia habita» (s. Tommaso, In De an., III, lect. 13ª, ed. Pirotta, n. 791). But this does not mean that the function of the intellect is exhausted in sensation. concept (v.) instead presents itself as interpretation and emergence, on the plane of being and of its absolute principles, of the empirical content of sensation. The intellect therefore manifests an essential noetic transcendence, as the discovery of the universal meaning and values of experience. Sensory knowledge therefore does not constitute an adequate principle of conceptual elaborations: it is not, as s. Tommaso expresses it, «totalis et perfecta causa intellectionis, sed magis quodammodo est materia causae» (Sum. Theol., 1ª, q. 74, a. 6, c., in fine). Equally irreducible to sensation is the knowledge that self-consciousness (v.) reflection (v.).
In its developments and systematic demands, s. relativism (v.) on both the theoretical and practical planes.