Idealism — A metaphysical position holding that reality is fundamentally mental, spiritual, or ideal in nature: what exists, or how we come to know it, ultimately depends on the mind. The term derives from the Greek idéa (“form,” “appearance”), echoing Plato’s intelligible Forms, though idealism as a modern current takes shape in the seventeenth and eighteenth centuries. Three major variants are usually distinguished. George Berkeley’s subjective idealism holds that only minds and their ideas exist: to be is to be perceived (esse est percipi); an apple is nothing more than the bundle of sensations of color, taste, and shape, with no material substance lying behind them. Immanuel Kant’s transcendental idealism, in the Critique of Pure Reason, argues that we cannot know things in themselves (Ding an sich) but only appearances—the world as organized by the forms of sensibility (space and time) and the categories of the understanding. Hegel’s absolute idealism, in turn, claims that the real is the rational and that reality is the development of Spirit (Geist), which progressively comes to know itself in history. By way of example, for Berkeley a tree in an uninhabited wood “exists” only insofar as it is perceived—ultimately by the divine mind. Idealism stands opposed to realism, which affirms a world existing independently of the mind, and to materialism, which reduces everything to matter.
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