DUALISM. – From the Latin dualis (derived from duo), it is any orientation or system which, in its general interpretation of the universe, or in a particular order of realities, facts, or phenomena, admits the existence of two heterogeneous and opposed principles. Thus, for example, any system that upholds the radical irreducibility of God and the world, matter and spirit, being and thought, is dualist. The term, today used in various and multiple senses, is first found applied to the Persian religion in Th. Hyde, Historia religionis veterum Persarum eorumque magorum (Oxford 1700), chap. 9: Mazdeism, in fact, later reappearing in Manichaeism with the fundamental doctrine of the two supreme independent principles, good (Ormuzd) and evil (Ahriman), presents a religious-metaphysical d. of universal and absolute order; for the specific content of this form of d., which always remains one of the term’s principal points of reference, V. MANIERISMO.
In the history of philosophical thought, d., as a system of interpreting reality and its manifestations opposed to monism, appears very early, subsequently taking multiple forms according to the various formal aspects of reality and the different order of facts examined by philosophical inquiry. An essential classification, though not complete in its most particular and specific applications, distinguishes cosmological-metaphysical, anthropological (psychological), epistemological (logical), ethical, and religious d. The conception of the world in the Pythagorean school (6th cent. B.C.) is dualistic. Having located the most intimate and essential value of reality in numbers and their relations, the Pythagoreans also believed that they had found in an opposition of mathematical order the root of the various antagonistic aspects presented by things: the immanent antithesis of finite-infinite, limited-unlimited, odd-even that lives in numbers expresses the radical dualistic opposition of reality, to which every other form of opposition in the physical, metaphysical, and ethical spheres is reduced, e.g. light-darkness, perfect-imperfect, good-evil. Cosmological d., in a form displaying analogies with the fundamental doctrine of Persian d., appears in Empedocles (5th cent. B.C.), who traces all bodily movements and phenomena back to two primordial opposing forces or principles, Love (φιλία) and Hatred (νεῖλος). Shortly thereafter, Anaxagoras, rising above the essentially naturalistic inquiry of the early Ionians, posits, as an explanation of the world, an ordering rationality (νοῦς) alongside passive matter. This metaphysical-theological d. was not overcome; indeed, it was expressed in more mature forms in the greatest of Greek speculation: in both Plato and Aristotle, eternal and passive matter would remain as an absolute position confronting the supreme creative and ordering intelligence.
But in Plato the dualistic moment is also essential in relation to the remaining motifs of his philosophical speculation: the intelligible world, separate from and opposed to the sensible world (the antecedents of this epistemological d. are found in Socrates and in pre-Socratic speculation itself, particularly in Eracilio and Parmenide), and the pre-existent soul violently joined to the body constitute the most radical expressions of the epistemological and anthropological d. of Platonism. And despite the correction introduced by Aristotelianism, the dualistic orientation of Plato’s philosophy would pass, with predominantly ethical-religious resonances, into Stoicism, Hellenistic speculation, and Neoplatonism, which would accentuate, in different forms, the radical opposition between matter and spirit, soul and body, senses and reason, passions and freedom. The particular opposition proclaimed by Gnosticism between the God of the Old and the God of the New Testament is an analogous expression of this form of d. A reflection of Platonic d. also seems at times to emerge in certain currents of Christian asceticism, where the contrast between flesh and spirit, nature and grace, is excessively intensified to the detriment of the harmony and living psychological unity of the person.
In medieval thought, a singular d., which would also repeatedly find echoes in Christian speculation during Humanism and the Renaissance, is offered by the Averroist theory of the “two truths,” of reason and faith, independent of and at times contradictory to one another.
In modern philosophy a rigid anthropological d. is taken up again with Descartes: having affirmed the radical opposition between spatiality (res extensa) and consciousness (res cogitans), Cartesian thought once again breaks the natural unity of the human composite, to the benefit of an excessive spiritualism that reproduces Plato’s dualistic theory in a new form. It is well known how Cartesian d. influenced the antithetical position of Spinoza’s monism, in which matter and spirit, spatiality and consciousness, are reduced to mere expressions or attributes of one and the same substance. In Kant, on the other hand, a radical epistemological d. is asserted through the separation introduced between reality and thought, datum of experience and transcendental form, phenomenon and noumenon: a d. that reappears in the moral theory of the author of criticism, with the irreducible opposition established between nature and morality, ethical value and finality.
Alongside these excessive forms of d., there is a moderate expression of it that imposes itself upon objective philosophical speculation and that traditional philosophy continues to defend against the extreme affirmations of both materialistic and spiritualistic monism. First of all, in the metaphysical-theological sphere, the duality of finite and infinite, contingent and necessary, world and God is a positive result of rational inquiry into the data offered by reality and experience: this d. is fundamental in Christian philosophy, in opposition to the various forms of monistic pantheism.
In the psychological sphere, traditional philosophy, while rejecting Platonic-Cartesian extremism, nevertheless affirms the essential distinction and transcendence of the human soul over the merely physical-physiological forces and activities of matter, thus rejecting all materialistic solutions to the anthropological problem, in which the most certain ethical-religious values of the human person are irreparably compromised. In parallel and consequently, a temperate epistemological d. is also affirmed in the recognition of the intellect’s superior value and function, essentially distinct from sensibility, though in intimate and constant relation with II. Furthermore, traditional thought opposes the transcendental idealism of modern philosophy with the d. of being and thought, subject and object, as the immediate result of critical-metaphysical inquiry into the content of experience. Finally, in the moral sphere, Christian philosophy, while denying the Kantian opposition between the subordinate values of the pleasant and the useful and ethical value, nevertheless affirms their essential heterogeneity, recognizing morality, against eudemonism (v.), as occupying an absolute and unconditional position. V. CONOSCENZA; DIO; IDEALISMO; MONISMO; PANTEISMO.