SENSO COMUNE. – The expression has two principal meanings in philosophy, one psychological and the other epistemological. In psychology, s. c. is the internal sense that effects the unification and discrimination of external sensations and their objects. In epistemology, in its principal historical sense (Reid and his school), it is the original and universal faculty of the human spirit to apprehend and formulate, prior to philosophical reflection, necessary or self-evident truths, whether factual or foundational. From this historical epistemological meaning have arisen parallel senses in current usage: s. c. as the complex of the principles or fundamental truths of reason; and s. c. as the natural faculty, common to every normal human being, of sound theoretical and practical judgment.
I. PSYCHOLOGY
The theory of common sense as the central faculty of sensibility received its definitive formulation only in medieval scholasticism: there it is understood as the first of the internal senses, which effects, from both the subjective and objective points of view, the unity of the various sensations: «sensus communis est quaedam facultas ad quam terminantur immutationes omnium sensuum» (s. Tommaso, In II De an., lect. 13, n. 390; cf. Sum. Theol., 1ª, q. 78, a. 4 ad 1). Common sense thus serves, within the sphere of sensibility, as the synthetic principle, in the unity of consciousness, both of the manifold data of sensations and of the sensitive functions themselves, «a quo etiam percipiantur actiones sensuum, sicut cum aliquis videt se videre» (ibid., ad 2; cf. In III De an., lect. 3). In the Aristotelian texts, however, the theory of common sense did not present itself free from uncertainties. Basing themselves on a passage from the De an., III, 1, 42 and 27: «of the common sensibles we already have a common sensation» (τῶν δὲ κοινῶν ἦδη ἔχομεν αἰσθησιν κοινήν), Albertus Magnus and, more recently, Zeller, Baeumker, Ross, Cassirer, and De Corte held that in Aristotle common sense is the perceptive faculty of the common sensibles (dimension, figure, movement, etc.; Sertillanges (St Thomas d'Aquin, II, 4th ed., Paris 1925) and others attributed the same doctrine to s. Tommaso, but on the basis of a passage from the opusculum De potentiis animae, which is not authentic). Against the exegesis of Albertus Magnus and Zeller stand Trendelenburg, Brentano, and Waddington (cf. the careful exposition and discussion in C. Fabro, Percezione e pensiero, Milan 1941, p. 60 ff.: the Thomistic interpreta-tion is demonstrated there—not only by the De somno et vig., 2, 455 a 12, where the expression σπανή δύναις seems to have the same meaning as the « sensus communis » of s. Tommaso—but also by the fundamental Aristotelian principle that the common sensibles are objects «per se» of several senses and not of a sixth sense). The medieval meaning of common sense is already found in s. Agostino, who in the De lib. arb., II, chap. 3, speaks of the « sensus interior », which « omnibus [sensibus externis] præcest ».
Later (Campanella, the Suárezian school, Mercier, Fröbes, etc.), the existence of common sense as a special faculty, distinct from the individual external senses, was contested, since it was held that awareness of seeing, hearing, etc., as an immediacy of consciousness, is a modality inherent in the sensory act itself, while, if reflective consciousness were involved, it would belong to the higher spiritual functions. Aristotle himself already seems to affirm that each sense senses its own act (De an., II, 425 b 15; cf. Mér., XI, 9, 1074 b 35: intellect and sense can, incidentally, ἐν τεχάργῳ, apprehend themselves). Modern psychology admits that the synthetic unity of the various sensitive functions finds its basis in the fundamental unity of consciousness and in the centrality of the physiological processes conditioning II. Common sense in the medieval meaning must not, however, be confused with the « coenesthesia » of modern terminology, which indicates rather the fundamental tactile sensibility through which one becomes aware of one’s own body and of its general biological functions and conditions.
II. GNOSEOLOGY
In the gnoseological sense, common sense was of fundamental importance in Th. Reid (v.) and in his school. For Reid, who opposes Humean empiricism and Berkeleyan immaterialism, the fundamental principles of every act of reasoning and of every science are, in a certain sense, connatural with the mind; and they are connected with perception, which is not apprehension of “ideas” (against Berkeley), but intuitive knowledge and the immediate presence of the object: “The most immediate conclusions that reason draws from perception form common sense, the more remote ones science” (Inquiry, chap. 6, sect. 20). Common sense is therefore the essential capacity of the spirit, prior to its reflective-scientific moment, to formulate universal and necessary propositions, and thus, as it were, the very principle of theoretical truth. Its maxims are those that prudent men follow in practice and in life, and at the same time the original principles according to which truth is distinguished from falsehood, without which certainty is impossible. It lies at consensus (v.) of every human consciousness concerning the first theoretical-practical truths. This doctrine, whose beginnings may be traced in the σπανή δύναις: of the Stoics (the idea was emphasized by Cicero: cf. De nat. deor., I, 17 and De orat., I, 3; De leg., I, 10), had already found a partially analogous expression in Shaftesbury’s (v.) “taste” or moral and aesthetic “sense,” and was developed by the continuators of the Scottish school (J. Oswald, Appeal to common sense in behalf to religion [1766]; D. Stewart, Elements of the philosophy of human mind [1792]; Th. Brown, Lectures on the philosophy of human mind [1920]; A. Fergusson; later, with the incorporation of contrasting Kantian motifs, W. Hamilton); opposition to it, on the other hand, constitutes one of the fundamental—perhaps the most fundamental—tenets of Millian thought (v. MILL. STUART 1). The meaning, if not the term, of common sense is moreover, in a certain sense, implicit in all the specific forms of rationalism ([v.] Plato, Plotinus, Descartes). For Leibnitz (v.), from common sense—“c’est-à-dire de l’esprit même”—come the ideas of space, extension, figure, motion…, Aristotle’s common sensibles (cf. Nouveaux essais..., II, chap. 5). Kant (v.) speaks of common sense as the presupposition of universally valid aesthetic judgments: it is to be understood as “common feeling”; it is not a special sense, “but only the effect of the free play of our cognitive faculties” (Kritik d. Urtellkraft, part 1ª, sect. 1ª, I, I, §§ 20-22; Italian trans., Bari 1938, pp. 79-82). F. Lamennais (v.) elevated common sense into the sole criterion of certainty, as an expression of general and common reason.In neo-Scholasticism, common sense has for the most part been accepted in a positive sense, with a meaning analogous to Reid’s, although less systematic: “sens commun ou intelligence naturelle,” “la raison spontanée et primitive” (R. Garrigou-Lagrange, op. cit. in the bibliography, p. 1, 15); it would therefore indicate the natural manner of thinking and judging proper to the human spirit, to which, on the theoretical plane, corresponds “that natural and objective realism… which is, one might say, in Bergson’s words, ‘la métaphysique naturelle de l’intelligence humaine’” (ibid., pp. 18-19). It is approximately in this sense that Aristotelian-Scholastic metaphysics is sometimes described as the “philosophy of common sense.”
An objective evaluation cannot fail to recognize a positive significance in common sense insofar as thought is universal and determinate. Eracilito (v.) already asserted: “thought is common to all” (Diels, frg. 113; cf. Mullach, I, p. 322). There is at least one notion—the concept of being-non-being—which belongs to the very essence of thought and universally grounds the first principles of every human discourse. Although these principles do not yet, in themselves, constitute elements of a systematic metaphysical conception of being and nature, they nevertheless lie at the basis of every attempt that reflective thought undertakes for this purpose. If, on the other hand, by common sense one means the more or less extensive body of ideas, opinions, and even principles universally shared by a historical period, its significance as truth remains in itself problematic. Common sense, in this acceptation, is in fact at least partly a function of customs, culture, civilization, and history; nor are its universality and necessity fixed, since it receives and slowly assimilates new ideas, conceptions, and systems, more or less transforming them. Common sense, understood in this way, therefore cannot claim, from the theoretical point of view, an unconditional authority, and its significance must be clarified by reflective thought, which determines its foundations, conditions, and causes.