In philosophy, idealism is the group of metaphysical philosophies which assert that reality, or reality as humans 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. In contrast to materialism, idealism asserts the primacy of consciousness as the origin and prerequisite of material phenomena. According to this view, consciousness exists before and is the pre-condition of material existence. Consciousness creates and determines the material and not vice versa. Idealism believes consciousness and mind to be the origin of the material world and aims to explain the existing world according to these principles.