Idealism

Idealism is the theory in the philosophy of mind that holds that mind is the ultimate stuff of reality, and matter depends on mind for its existence. Metaphysical idealism holds that only mind or mental substance exists; epistemological idealism may acknowledge that an external world might exist, but says that we can have no certain or direct knowledge of it. It is opposed to materialism, which holds that matter is the ultimate stuff of reality, and mind depends on matter for its existence, and dualism, which holds that mind and matter are both separate and independent things, and neither is reducible to the other.

There were historically three main movements of idealism: in early modern Britain, most notably with George Berkeley, who advanced metaphysical idealism as a counter to skepticism about the existence of an external world; German Idealism in the late 18th and early 19th centuries, starting with Immanuel Kant's epistemological idealism and getting weirder; and British and American idealism in the latter part of the 19th century, with leading figures including F. H. Bradley and J. M. E. McTaggart.

Idealism is frequently associated with the idea that material reality is somehow unreal. Many idealists have indeed believed this - famously, McTaggart claimed that the notion of time was so self-contradictory and incoherent that it must be illusory. But not all idealists agree with labeling material reality as "unreal"-an alternative idealist view is that while it does not possess the same ultimate reality, the independent self-existence which mind possesses, it nonetheless is real for what it is.

Idealism was the predominant school in British philosophy at the beginning of the twentieth century. Under attack from G. E. Moore and Bertrand Russell, it swiftly declined and was overtaken by logical positivism, among others, although Neo-Kantianism was popular in German in the early 20th century, R. G. Collingwood upheld the idealist flag at Oxford University in the early 20th century until World War II, and some versions of epistemological idealism persisted. Nevertheless, idealism is certainly not as prominent and plentiful now as it once used to be. Postmodern philosophy, such as that of Gilles Deleuze, is sometimes accused of being idealism (for denying scientific truth, the physical world, etc), but it doesn't have much in common with older forms of idealism.