In philosophy, idealism is the family of views which assert that reality, or reality as we can know it, is fundamentally mental, mentally constructed, or otherwise immaterial. Epistemologically, idealism manifests as a skepticism about the possibility of knowing any mind-independent thing. As an ontological doctrine, idealism goes further, asserting that all entities are composed of mind or spirit. Idealism thus rejects physicalist and dualist theories that fail to ascribe priority to the mind.
Religious and philosophical thought privileging the immaterial or supernatural over the material and natural is ubiquitous and ancient. However, the earliest extant arguments that the world of experience is grounded in the mental derive from India and Greece. The Hindu idealists in India and the Greek Neoplatonists gavepantheistic arguments for an all-pervading consciousness as the ground or true nature of reality. In contrast, the Yogācāra school of Buddhism based their “mind-only” idealism to a greater extent on phenomenological analyses of personal experience. This turn toward the subjective anticipated empiricists such as George Berkeley, who revived idealism in 18th-century Europe by employing skeptical arguments against materialism.
Beginning with Immanuel Kant, German idealists such as G. W. F. Hegel, Johann Gottlieb Fichte, Friedrich Wilhelm Joseph Schelling, and Arthur Schopenhauerdominated 19th-century philosophy. This tradition, which emphasized the mental or “ideal” character of all phenomena, birthed idealistic and subjectivist schools ranging from British idealism to phenomenalism to existentialism to postmodernism. The historical influence of this branch of idealism remains central even to the schools that rejected its metaphysical assumptions, such as Marxism, pragmatism, and positivism.