Idealism is a name adopted by several schools of philosophy, all of which in some way assert the primacy of ideas, either as the sole authentic stuff of reality or as the only medium through which we can have knowledge or experience of the world. Idealisms are commonly contrasted both with the various types of realism and with philosophical materialism. They are often associated with methodological rationalism because they usually seem to owe more in reasoning upon a priori principles than to any appeal to experience. The idealism of Plato, in which ideas were held to have an external objectivity, is unrepresentative of modern varieties, of which that of George Berkeley is archetypal. Kant and Hegel were foremost in the German idealist tradition, while T. H. Green, F. H. Bradley, and J. Royce were representative of more recent-speaking idealists. Idealism has, however, been in eclipse since the start of the twentieth century.