RATIONALISM. — A relatively recent philosophical term (it entered usage with English deism [v.] in the seventeenth century) and one rich in meanings. Three fundamental senses may be distinguished: 1) the metaphysical sense; 2) the epistemological sense; 3) the religious sense.
1. Metaphysical sense
Everything has a reason for being, and there is nothing, at least in principle, that is not rational. Reason (v.) is, in brief, the first principle of universal intelligibility, and everything that exists, in itself even if not for us, is reducible to the essential laws of rational thought, understood as the principle of the reason of things, even if the inadequacy of our cognitive means may prevent us from fully grasping this profound rationality of the universe in its unity and totality. In this sense, r. may be pantheistic, theistic and, if the term is permissible, semi-pantheistic: pantheistic if it identifies the rationality immanent in the world with God himself (Stoicism, Plotinus, Spinoza, Hegel, etc.); theistic if it makes it derive from God’s creative act, God being transcendent with respect to the world (Plato, s. Augustine, s. Thomas, Vico, etc.); semi-pantheistic if it does not identify God with the principle of reason immanent in the world, but makes the world itself, in its universal “harmony,” the “best of all possible worlds,” which God could not but create out of moral necessity (Leibniz). In all these cases, however, it is admitted that: a) the world has an order and an end, and nothing in it is entrusted to chance; b) if it seems otherwise to us, this is due to the imperfection of our knowledge and to our limitations as finite and contingent beings, who are unable to discern the great “economy” of the universe, attributable either to the immanent Reason that governs it (pantheistic thesis) or to Providence, which brings about a mysterious divine plan (theistic thesis).2. Epistemological sense. — The sole source of knowledge of truth is reason, the essential and exclusive faculty for this purpose. In this sense, r. is opposed to all forms of sensationalism (v.) and empiricism (v.), which take as sources of truth (and of every truth) the associations, classifications and schematizations that the intellect makes of sense-data. From this point of view, one may speak of a r. Socrates (v.) and Plato (v.) opposed Sophists (v.); Leibniz (v.) LOCKE, JOHN (v.), etc. Naturally, not all forms of epistemological r. display an equal degree of rigidity and exclusiveness. In antiquity, this character belongs to the r. of the Eleatic school and above all of Parmenides, who considers all sense experience illusory and deceptive: Justice, which “possesses the keys that open and close” (that is, reason), on receiving the philosopher, declares two things to him: that there is the realm of science, which is “well-rounded truth,” and the realm of opinions, which deserve no credence—that is, being, which is intelligible and of which there is truth, and not becoming (the sensible), which is appearance and of which there is only opinion (Sextus Emp., Adv. math., VII, 111 ff.). One must judge not with “the eye that does not see” and with “the hearing that resounds with illusory sounds,” but with “reason” (ibid., VII, 114), the sole faculty that affirms the unity of being. Socrates and Plato temper the intransigence (and abstractness) of Eleatic r., and neither of them denies the importance of sense or excludes sensation from the cognitive process. With Plato, however, r. assumes the essential character of “innatism” (v.), which, with various nuances or developments, will be preserved by the entire Platonic current: there exist in the human soul forms of knowledge-principles or rational forms, etc., prior to all external experience, reflection (v.) discovers. Sensation is merely “the occasion” for awakening in the soul the innate, forgotten knowledge (v. especially the Meno). This enables Plato neither to exclude nor to devalue the intermediate degrees of knowledge (v. especially the Theaetetus), but it does not allow him to grasp the true value of the sensible and of sensation. For him, true knowledge is intellectual (νόησις) and discursive (διάνοια) knowledge, directed toward the Ideas, entities that always remain identical to themselves and that can be apprehended only through thought (Phaed., 79 a), the sole faculty that enables us to acquire truth and wisdom (ibid., 66 a; Resp., 508 d). Aristotle (v.) eliminated Platonic innatism and vindicated the value of sense knowledge as the origin of all our knowledge, while always assigning primacy to rational truth. “Of all things we have certainty either through syllogism or through induction. We learn either through induction or through demonstration. Demonstration proceeds from universals, induction from particulars” (Analyt. pr., II, 23, 68 b 13). These two classical forms of r. recur in Christian Platonism (s. Augustine, s. Bonaventure) and in Christian Aristotelianism (s. Thomas), developed respectively in the sense, in the former case, of the “interiority” of truth (distinct from innatism), and, in the latter—which contains strong Platonic-Augustinian elements—in the sense that, in addition to ratio, it admits (as Augustine does) intellectus, a superior and intuitive faculty of knowing, although the one and the other are not two distinct powers: “Etsi intellectus et ratio non sint diversae potentiae, tamen denominantur ex diversis actibus. Intellectus enim nomen sumitur ab intima penetratione veritatis, nomen autem rationis ab inquisitione et discursu” (Sum. Theol., 2ᵃ-2ᵃᶜ, q. 49, a. 5 ad 3).
But the term rationalism acquired a precise philosophical meaning, the one now in use, only with so-called modern rationalism, Descartes (v.) to Wolff (v.): there exist in us a priori principles (innate, even if only in a “virtual” state), evident in themselves, of which every true cognition is a necessary consequence, to which the senses contribute nothing. It should be borne in mind that modern rationalism develops simultaneously with the formation of modern science: rationalism and scientism are inseparable. Hence the demand for a purely rational truth, capable of dominating and ordering the confused material of sensory experience. But neither rationalism nor empiricism (v.), which opposes it, yet possesses a critical concept of experience itself, and both confuse it with the “empirical datum”: rationalism therefore loses itself in an apriorism of forms without content, and empiricism in the mass of sensory data without a valid rational form for the purposes of discovering and attaining truth. Rationalism also signifies the rational domination of reality and the autonomy of reason itself from every other authority: if reason is innate in man and the principles of all truth are innate in it, then it is independent of tradition, rests upon itself, rejects everything that cannot be reduced to it, “criticizes” every other authority, constructs its “natural” right and its “natural” morality (neither of them any longer of divine origin), and its “natural” religion (without dogmas and without Revelation). For rationalism, it is enough for reason to be free to realize itself fully for total truth and an entirely rational, wholly complete, and absolutely perfect body of knowledge to be achieved. Thus rationalism presents itself as a revolt against tradition (including religious tradition) and history, from its founder R. Descartes onward, whose Discourse on Method is its manifesto (v. especially part 2ᵃ). From the epistemological point of view, the position of rationalism seems well defined by Leibniz: “The knowledge of necessary and eternal truths is what distinguishes us from mere animals and gives us reason and the sciences, raising us to knowledge of ourselves and of God” (Monadology, no. 29), without sensory experience having anything to do with it: “Pure and bare reason, distinguished from experience, deals only with truths independent of the senses” (Theodicy, Discourse on Conformity, 1). Thus rationalism, science (v.) and its development, dogmatically assumes as the typical truth of knowledge the physico-mathematical truth: the rational construction of the world, deduced a priori through analysis and culminating in a Cause or a Law, identified with God, who guarantees the perfect functioning of that “machine” which is the cosmos. Hence, “the critical position of rationalism is not a critique of reason, but of whatever cannot be reduced to rational cognition: the absoluteness of reason, assumed dogmatically, is critically employed as the measure by which everything must be measured... For rationalism everything is rationally clear, and what is obscure is a lower degree of knowledge; all problems are well defined and resolved: reason conforms to the natural order, and the natural order satisfies the demands of reason. In a world without philosophical enigmas, religious mysteries are no longer necessary, being the product of fanaticism and superstition, as barbarous scientism and the superficial philosophism of the Enlightenment conclude [v.]” (M. F. Sciacca, Objective Interior Life, Milan 1952, pp. 53–54).
It is precisely this “reason” of rationalism that profoundly criticizes empiricism, objecting that all human knowledge derives from sensory experience, which constitutes the unsurpassable limit of reason. Kant’criticism (v.) belongs within this dispute; in it rationalism acquires a new meaning in relation to the new meaning that Kant gives to the term “experience” (v.). Experience is not the empirical datum: this is only the content of experience, which is possible because the spirit possesses reason, that is, a system of a priori forms that organize and systematize empirical data. Experience is therefore a synthesis of the a priori form and the a posteriori empirical datum, which finds its order in the form and gives the form its content. Consequently: a) the a priori principles of rationalism from Descartes to Wolff cease to be innate truths and, with Kant, become “a priori” conditions that the intellect applies to empirical or sensory data in such a way as to raise sensory knowledge to the level of rational knowledge and construct that synthesis which is experience; b) “knowledge through reason” (Vernufferkantin) and a priori knowledge are “one and the same thing” (einerlei), insofar as reason contains the principles that provide a priori knowledge (Critique of Pure Reason, introduction, § 7); c) but since the principles are transcendental a priori conditions and forms, their validity remains limited to empirical experience or the phenomenon; d) and thus Kant, like empiricism, takes the sensible as the limit of reason and can no longer avoid metaphysical agnosticism. Rationalism thus, with Kantian criticism, comes to be identified with the possibility of physics and mathematics as sciences, while, on the other hand, it fails to avoid the subjectivity of knowledge, given that the a priori is not a truth, but only a condition (the transcendental activity of the subject) of experience.
After Kant, but through the development of Kant, Hegel (v.) makes Reason the metaphysical principle, identifying the “real” and the “rational.” For Hegel too, the Idea is transcendental, but no longer a function and condition of experience; rather, it is a metaphysical entity which, through the law of dialecticism, actualizes itself and resolves all reality within itself—not merely phenomenal reality—without any remainder in the thing-in-itself. agnosticism (v.) is thus eliminated, not because Hegel (and all transcendental idealism) establishes and resolves the problems of metaphysics, but because it dissolves metaphysics into logic, that is, being into thought. Accordingly, in Hegel, metaphysical and epistemological rationalism are identified, and dialecticism (the passage from one term to the other of the contradiction and the unity of contradictories; Encyclopedia, § 81) is at once the law of thought and of reality. Thus reason once again dogmatizes itself and, by positing itself as total truth, denies its own truth and every truth in the “irrationality” of its absoluteness and in the abstractness of panlogism.
3. Religious sense. — It should rather be called “irreligious,” given that so-called “natural” or “rational” religion amounts to a denial of religion, insofar as it reduces its entire content of truth “within the limits of reason.” Accordingly, religious r. is that doctrine or doctrinal attitude which admits of religion only those truths that can be rationally known. Strictly speaking, one cannot speak of a religious r. before Christianity, since there was no revealed and therefore suprarational and dogmatic truth. Religious r. begins with English deism, according to which religious truths are accepted not because they are revealed, but insofar as they are understood and justified by reason. Thus the truths of faith are denied, and religion is made a stage of reason itself or is dialectically resolved into philosophy (Hegel, Gentile), of which it is an inferior stage. A doctrine heterodox in every respect (and naturally condemned), since it denies Revelation and subordinates religion to reason; in fact and in principle it denies it, insofar as it denies dogma and the supernatural. In combating religious r., one must not fall into the opposite (likewise heterodox) excess of the “irrationality” of revealed truth (as though it were “absurd” to reason: Kierkegaard, Barth, etc.) fideism (v.), which, by denying reason, loses faith itself. Religious r. should not be opposed by religious “irrationalism,” since revealed truth is not contrary to reason, but above it, without contradicting or opposing reason. Indeed, it can be defended negatively by reason (by demonstrating the falsity of the contrary assertion), while remaining suprarational and dogmatic truth. V. also, for the theological aspects of r., GRAZIA; MISTERO; RIVELAZIONE; SOPRANNATURALE.
BIBL. For the authors cited, V. the corresponding entries. On modern r. in general, bibliographical indications in Überweg, III, p. 653 ff., 683 ff. In particular: K. Fr. Stäudlin, Gesch. des Rationalismus
and Supernaturalismus, Gottinag 1836; A. Tholuck, Gesch. d. Rational., Berlino 1865; H. Heussler, Der Rationalism. des 17. Jahrh., Breslavia 1885; C. Grube, Über den Rationalism. in der neueren engl. u. franzis. Philos., (diss.), Halle 1889; W. Pasing, Spinozae Rational. (diss.), Lipsia 1893; L. Ollé-Laprun, La raison et le rational., Parigi 1906; F. Enriquez, Scienza e r., Bologna 1912; M. Robertson, Rational., Edimburgo 1912; K. Girgensohn, Rationalis., Lipsia 1926; F. Enriquez-G. de Santillan, Le problème de la connaissance. Empirisme et rationalisme grecs., Parigi 1938; J. Marechal, Le point de départ de la métaphysique, cahier II, 2ᵉ ed., Bruxelles-Parigi 1942. An extensive article, particularly from the theological point of view, by C. Costantin, Rationalisme, in DThC, XIII, II, coll. 1688-1788. Michele Federico Sciseca