Idealism, in philosophy, is a metaphysical theory—that is, a theory about the nature of reality. According to metaphysical idealism, the external world consists of ideas that, being ideas, can exist only in the mind. According to this view, reality is thus mental or spiritual. The opposing philosophical view is called materialism. Materialists argue that reality consists of physical objects alone and that it is governed by purely physical forces.
In the early 1700’s, George Berkeley, an Anglican bishop and philosopher, claimed that the physical world was just a set of ideas or appearances in the minds of God and individual souls. For Berkeley, the physical world had no independent existence apart from the mind.
Initially, idealism strikes most people as absurd. The theory appears to deny what we all know, that the world of galaxies, mountains, trees, and skyscrapers exists. One story tells that Samuel Johnson, a famous English writer of the 1700’s, kicked a stone and uttered the words, “Thus I refute Berkeley!”
Most idealists would regard Johnson’s comment as unimportant. Berkeley claimed that he did not deny that the physical world existed or was real. His idealism is a theory about the nature of the physical world rather than its existence. Berkeley claimed that physical objects were real but that they could not exist without God and other spirits. For Berkeley, for something to exist, it had to be perceived by some spirit.
In the late 1700’s and 1800’s, the German philosophers Immanuel Kant and G. W. F. Hegel and other influential idealists tried to show that reality was spiritual or was dependent on minds without denying the reality of the physical world. In fact, idealists often argue that a reality which is totally separate from the mind could not possibly be known. From the idealist perspective, it is realism—the belief in the existence of physical things that are independent of the mind—that leads to doubt about the reality of the world. If the world had a nature and existence separate from our minds, it would seem to be difficult or impossible to know it. According to idealists, only idealism, by bringing the world into the mind, makes reality knowable.
Modern thinkers continue to debate the nature of reality. Metaphysical realists believe that reality is objective—that is, its existence and nature are independent of our minds. However, most metaphysical realists would agree that we can only know the world in the form in which it appears to us, and that the way the world appears to us depends on our minds, senses, and cultural traditions. Idealists would argue that these views cannot both be true. They resolve the conflict between these views by rejecting the idea that reality is independent of our minds.
