In the early history of philosophy, particularly in medieval thought, the term realism was used, in opposition to nominalism, for the doctrine that universals have a real, objective existence. In modern philosophy, however, it is used for the view that material objects exist externally to us and independently of our sense experience. Realism is thus opposed to idealism, which holds that no such material objects or external realities exist apart from our knowledge or consciousness of them, the whole universe thus being dependent on the mind or in some sense mental. It also clashes with phenomenalism, which, while avoiding much idealist metaphysics, would deny that material objects exist except as groups or sequences of sensa, actual and possible.

The Polemic Against Idealism

At the close of the nineteenth century, idealism was the dominant Western philosophy, but with the opening of the twentieth century, there was an upsurge of...