The view that perception is to be thought of in terms of the presence of mental state (or sometimes brain states), that represent the features of the world that is perceived. The view is alluring, but faces the problem that if these states are the only ones to which we can have direct access, then we cannot compare them with the features of the world they supposedly represent. It would be like comparing a portrait with a sitter, but without being given any access to the sitter except via the portrait. The representative theory of perception is generally attributed to Locke, who thought our ideas represent the primary qualities of bodies, and the charge that the theory leads to scepticism about the external world was pressed by Berkeley. The philosophy of perception is centrally concerned with the difficulties over the idea of a representative mental state. See also idealism, primary/secondary qualities, realism, representationalism.