- Idealism in philosophy, also known as philosophical idealism or metaphysical idealism, is the set of metaphysical perspectives asserting that, most fundamentally, reality is equivalent to mind, spirit, or consciousness; that reality is entirely a mental construct; or that ideas are the highest form of reality or have the greatest claim to being considered “real”. The radical latter view is often first credited to the Ancient Greek philosopher Plato as part of a theory now known as Platonic idealism. Other than in some Western philosophy, idealism also appears in some Indian philosophy, namely in Vedanta, one of the orthodox schools of Hindu philosophy, and in some streams of Buddhism.