REASON. — A philosophical term which, faculty (v.), has had a multiplicity of meanings throughout the history of Western thought, often giving rise to equivocations and misunderstandings. Probably the term ratio derives from ratus,
the participle of reor (to believe, to think), and before its properly philosophical use it meant calculation, proportion. Ratio corresponds both to νοῦς (Plato) and to λόγος, with this difference: νοῦς is properly the faculty or activity, whereas λόγος is the content of νοῦς (truth), or that which reason constructs (discourse, the totality of relations, etc.). It is appropriate to distinguish the two fundamental meanings of the term: reason as faculty (Vernunft) and reason as the object of knowledge (Grund).
I. R. AS FACULTY. — The two terms νοῦς and λόγος together adequately express the sense of r. as a discursive or ratiocinative faculty, capable of formulating proofs, combining concepts and propositions, and providing demonstrations. In this function it is regarded as proper to man (who, according to the celebrated Aristotelian expression, is ζῶον λογικόν), as St. Thomas says (In III Sent., dist. 25, q. 1, a. 1). «et Deo non convenit nec Angelis». In this sense intellect (v.), which is an intuitive activity, apprehensive of being and capable of grasping the first principles and the primary necessary truths of thought and life. These are not two faculties, as St. Augustine and St. Thomas unanimously maintain. Indeed, for St. Augustine, ratio and intellectus (or intelligentia) inhere naturaliter in the mens (De civ. Dei, XI, cap. 2); the intellectus is superior to the ratio (In Joann. Evang., tract. XV, 4, 19; and St. Thomas, Sum. Theol., 242⁶⁰, q. 45, 5 ad 3), insofar as it is inner vision (by which the mens perceives the truth, which reveals to it the divine light), the principle of understanding and the true eye of the soul (De ordine, II, cap. 2, n. 5; cap. 9, n. 26).
R., on the other hand, is aspectus animi, an organ of inquiry that discerns (analysis) and connects (synthesis), that is, the discursive faculty which applies itself to the sense that is inferior to it and to sensible things in order to judge them (De vera relig., cap. 29, n. 30). Spinoza (v.) too, r. is inferior to intuitive science: the former makes us see things sub quadam aeternitatis specie, the latter sub specie aeternitatis. Kant (v.) distinguishes between r. (Vernunft)—the faculty that enables us to know the principles of a priori knowledge—and pure r., the faculty that contains the principles enabling us to know something exclusively a priori (Crit. della r. pura, Introduz., § VII); between theoretical or speculative r., which is applied to pure knowledge and establishes and constructs science, and practical r., which contains the a priori principle of action or the rule of morality. Furthermore, Kant understands the term r. in the special sense of the higher faculty of the three metaphysical ideas of the soul, the world, and God (Cr. d. r. pura. Dialett. trascendentale, I, 1, sez. 1⁸). In this sense r. (Vernunft) is not opposed to experience (as in the first case), but is distinguished from and opposed to the intellect (Verstand). ROSMINIANI (v.), following St. Augustine and in order to combat Kantian transcendentalism, likewise distinguishes between r. and the intellect, or light of r.: the former is «the faculty of applying the idea of being», which is intuited by the intellect (Principi di sc. morale, cap. 1, art. 1). The post-Kantians made r. the absolute, intuitive of all reality, which identifies itself with it: GIACOBBI (v.) it is the faculty of grasping the supersensible; Schelling (v.) «it is the absolute» (Darstellung meines Syst. der Philos., in Sämtl. Werke, VI, p. 115); Hegel (v.) it is «the certainty of being all reality»; the universality and objectivity in itself and for itself of Self-Consciousness (Encicl., § 437).
Always in the sense of faculty, r. means judging well or rightly, that is, making proper logic (v.), and it also indicates, in modern rationalism and in Kant, the system of a priori principles, independent of experience; finally, it faith (v.) and to revealed and suprarational truth (for these latter three meanings V. RAZIONALISMO).
II. REASON AS AN OBJECT OF KNOWLEDGE
It is that which explains something in a twofold sense: ontological, as, for example, in “reason for being,” the “why” that explains and demonstrates the reason for a thing, the final cause and the formal cause; and epistemological, that is, the argument by which an assertion is upheld and justified. In the languageof the Scholastics, the ratio of a thing is its essence (ratio intellecta is the same concept considered objectively). It may also be used in a normative sense of justification: for example, in the expression “I have my reasons for doing or thinking so,” that is, the legitimate motives for acting and affirming in this way and not otherwise. In this sense, the reason for a proposition or thesis is that which justifies it and demonstrates its objective validity. Finally, the expression “being of reason” denotes that which has objective existence only in the mind (without this excluding the possibility that it may have a real foundation), as, for example, relations, negations, etc.
Contemporary philosophy has strongly criticized reason as an object of knowledge both in the ontological sense (denial of the final and formal cause) and in the epistemological sense: there are no arguments for necessarily demonstrating an assertion, since there are only “hypotheses” that are accepted (one or the other) according as they prove more or less suitable to a particular historical or practical situation (v. IRRATIONALISM; NEOPOSITIVISM; PRAGMATISM, etc).