Idealism in philosophy is a set of metaphysical perspectives that assert that reality is equivalent to mind, spirit, or ideas. It is the view that mind is the most basic reality and that the physical world exists only as an appearance to or expression of mind, or as somehow mental in its inner essence. Idealism is often used in such a way that it gets its meaning through what is taken to be its opposite, such as realism, materialism, dogmatism, and empiricism. There are two fundamental conceptions of idealism: metaphysical or ontological idealism, which asserts the ideality of reality, and formal or epistemological idealism, which holds that in the knowledge process, the mind can grasp only the psychic or that its objects are conditioned by their perceptibility. The founding fathers of idealism in Western thought are Berkeley, Kant, and Hegel.