1. a theory opposite to monism, holding that reality consists of two substances (e.g., mind and matter, body and soul). 2. in Platonic metaphysics, the belief that human being consists of soul and body, the latter being a prison in which the formerly all-knowing soul resides. 3. a theory running contrary to monotheism, holding that supernatural reality is of two forms, the one good and the other bad; Manichaenism is one such dualistic religious view.

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