A leading exponent of the substantial view was George Berkeley, an 18th century Anglican bishop and philosopher. Berkeley argued that there is no such thing as matter and what humans see as the material world is nothing but an idea in God’s mind, and that therefore the human mind is purely a manifestation of the soul. Few philosophers take an extreme view today, but the view that the human mind is of a nature or essence somehow different from, and higher than, the mere operations of the brain, continues to be widely held.
Berkeley’s views were attacked, and in the eyes of many demolished, by T.H. Huxley, a 19th century biologist and disciple of Charles Darwin, who agreed that the phenomena of the mind were of a unique order, but argued that they can only be explained in reference to events in the brain. Huxley drew on a tradition of materialist thought in British philosophy dating to Thomas Hobbes, who argued in the 17th century that mental events were ultimately physical in nature, although with the biological knowledge of his day he could not say what their physical basis was. Huxley blended Hobbes with Darwin to produce the modern materialist or functional view.
Huxley’s view was reinforced by the steady expansion of knowledge about the functions of the human brain. In the 19th century it was not possible to say with certainty how the brain carried out such functions as memory, emotion, perception and reason. This left the field open for substantialists to argue for an autonomous mind, or for a metaphysical theory of the mind. But each advance in the study of the brain during the 20th century made this harder, since it became more and more apparent that all the components of the mind have their origins in the functioning of the brain.
Huxley’s rationalism, however, was disturbed in the early 20th century by the ideas of Sigmund Freud, who developed a theory of the unconscious mind, and argued that those mental processes of which humans are subjectively aware are only a small part of their total mental activity. Freudianism was in a sense a revival of the substantial view of the mind in a secular guise. Although Freud did not deny that the mind was a function of the brain, he held the mind has, as it were, a mind of its own, of which we are not conscious, which we cannot control, and which can be accessed only though psychoanalysis (particularly the interpretation of dreams). Freud’s theory of the unconscious, although impossible to prove empirically, has been widely accepted and has greatly influenced the popular understanding of the mind.