DUALISM. — From the Latin *dualis* (derived from *duo*), dualism is any approach or system that, in the general interpretation of the universe or in a particular order of reality, facts, or phenomena, admits the existence of two heterogeneous and opposing principles. For example, a dualist system defends the radical irreducibility of God and the world, of matter and spirit, of being and thought. The term, now used in various and manifold ways, is first found applied to Persian religion in Th. Hyde, *Historia religionis veterum Persarum eorumque magorum* (Oxford 1700), ch. 9: Mazdaism, which later reappeared in Manichaeism with the fundamental doctrine of two supreme independent principles, the good (Ormuzd) and the evil (Ahriman), presents a religious-metaphysical dualism of a universal and absolute order; for the specific content of this form of dualism, which remains one of the principal references of the term, see MANICHAEISM.
In the history of philosophical thought, dualism, as a system of interpreting reality and its opposing manifestations in contrast to monism, appears very early, later taking on multiple forms depending on the various formal aspects of reality and the different orders of facts examined by philosophical inquiry. An essential classification, though not exhaustive of the most particular and specific applications, distinguishes cosmological-metaphysical dualism, anthropological (psychological), gnoseological (logical), ethical, and religious dualism. Dualistic is the conception of the world in the Pythagorean school (6th century B.C.). By placing the most intimate and essential value of reality in numbers and their relationships, the Pythagoreans also believed they had found in a mathematical opposition the root of the various antagonistic aspects presented by things: the immutable antithesis of finite-infinite, limited-unlimited, odd-even that exists in numbers expresses the radical dualistic opposition of reality to which all other forms of opposition in the physical, metaphysical, and ethical realms are reduced, e.g., light-darkness, perfect-imperfect, good-evil. Cosmological dualism, in a form that presents analogies with the fundamental doctrine of Persian dualism, appears in Empedocles (5th century B.C.), who reduces all movements and corporeal phenomena to two primordial and antithetical forces or principles, Love (φιλία) and Strife (νείκος). Shortly afterward, Anaxagoras, rising above the essentially naturalistic inquiry of the early Ionians, posits, to explain the world, alongside passive matter a rational ordering principle (νοῦς). This is a metaphysical-theological dualism that will not be surpassed; indeed, it will be expressed in more mature forms in the greatest Greek speculation: both in Plato and Aristotle, eternal and passive matter remains as an absolute position over against the supreme intelligence, art, and ordering principle.
But in Plato the dualistic moment is essential also in relation to the remaining motifs of his philosophical speculation: the intelligible world, separate and opposed to the sensible world (the precedents of this gnoseological dualism are found in Socrates and in pre-Socratic speculation, particularly in Heraclitus and Parmenides), the pre-existent soul violently conjoined with the body, constitute the most radical expressions of the gnoseological and anthropological dualism of Platonism. And despite the correction introduced by Aristotelianism, the dualistic orientation of Plato’s philosophy will pass, with predominantly ethical-religious resonances, into Stoicism, Hellenistic speculation, and Neoplatonism, which will accentuate, in various 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 Testament and the God of the New Testament is an analogous expression of this form of dualism. A reflection of Platonic dualism seems at times to surface also in some currents of Christian asceticism, where the contrast between flesh and spirit, nature and grace is sometimes so exacerbated as to the detriment of the harmony and living unity of the psychological person.
In medieval thought, a singular dualism—which would echo repeatedly in Christian speculation during Humanism and the Renaissance—is offered by the averroistic theory of the “two truths,” of reason and of faith, independent and at times contradictory to one another.
In modern philosophy, Descartes revived a rigid anthropological dualism: by affirming the radical opposition between spatiality (res extensa) and consciousness (res cogitans), the natural unity of the human composite is once again shattered in Cartesian thought, to the benefit of an excessive spiritualism that reproduces in a new form the dualistic theory of Plato. It is well known how Cartesian dualism influenced the antithetical position of Spinoza’s monism, in which matter and spirit, spatiality and consciousness are reduced to mere expressions or attributes of a single substance. In Kant, by contrast, a radical gnoseological dualism is affirmed with the separation introduced between reality and thought, the given of experience and the transcendental form, phenomenon and noumenon: a dualism that reappears in the moral theory of the author of the Critique, with the irreducible opposition established between nature and morality, ethical value and finality.
Alongside these extreme forms of dualism, there is a moderate expression of it that imposes itself upon objective philosophical speculation and that traditional philosophy continues to defend against the extreme assertions of both materialistic and spiritualistic monism. First, in the metaphysical-theological realm, 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 is a fundamental dualism in Christian philosophy, in opposition to the various forms of monistic pantheism.
In the psychological realm, traditional philosophy, while rejecting Platonic-Cartesian extremism, nevertheless affirms the essential distinction and transcendence of the human soul over the purely 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. Parallel to and consequent upon this, a tempered gnoseological dualism is also affirmed in the recognition of a superior value and function of the intellect, essentially distinct from sensibility, even if in intimate and constant relation with II. Moreover, against the transcendental idealism of modern philosophy, traditional thought opposes the dualism of being and thought, subject and object, as an immediate result of critical-metaphysical inquiry into the content of experience. Finally, in the moral realm, Christian philosophy, while denying the Kantian opposition between the subordinate values of the pleasant and the useful and the ethical value, nevertheless affirms their essential heterogeneity, recognizing in morality, against every form of hedonism and eudemonism (see), an absolute and unconditional position.
See CONOSCENZA; DIO; IDEALISMO; MONISMO; PANTEISMO.