In the philosophy of mind, mentalism is the view that the mind and mental states exist as causally efficacious inner states of persons. The view should be distinguished from substance dualism, which is the view that the mind and the body (or brain) are two distinct kinds of things which nevertheless interact with one another. Although this dualistic view of the mind–body connection entails mentalism, mentalism does not entail dualism. Jerry Fodor and Noam Chomsky have been two of mentalism's most ardent recent defenders.
In metaphysics, mentalism is the view that metaphysics is primarily concerned with entities in the mind (See also conceptualism), and denotes the general orientation beginning with William of Ockham and reaching a climax in the idea- or representation-first philosophers (what John Sergeant calls 'Ideism') common in the Early Modern period, including such philosophers as René Descartes, John Locke, George Berkeley, David Hume, etc. who make the faculties of the mind and their activities the starting point for their philosophical projects.
In linguistics, mentalism represents rationalistic philosophy (as opposed to behaviouristic).