Plato and other thinkers of antiquity were not much interested in mind. They were interested in “the soul,” conceived as a non-material composite of reason, passion and appetite. Plato wished to demonstrate in his Phaedo and Phaedrus that the soul is immortal, and that ethical perfection consists in the harmony of its parts.
Scientific interest in mind qua organ of thought owes itself to René Descartes, who argued in his Meditations (1641) that mind is thinking substance and matter extended substance or space. This dualism looks plausible because mental and material properties seem exclusive; we do not describe thoughts as having, say, colour or weight. But dualism involves a difficulty that stumped Descartes: how, if mind and matter are so different, can they interact?
The intractability of this problem led his successors to abandon dualism. There can be only one kind of substance, they said, either mental (idealism) or material (materialism). Idealism is a minority view; its most famous exponent is Bishop Berkeley in Principles of Human Knowledge (1710). Materialism is the dominant thesis; it says that however we understand minds, they must fit into our theories about the physical world.
The toughest version of materialism is BF Skinner’s Science and Human Behaviour (1953); it claimed that all mental phenomena (thought, thirst and so on) can be explained in terms of behaviour. Gilbert Ryle’s The Concept of Mind (1949) argued that all theories of mind since Descartes have been bedevilled by the myth of a “ghost in the machine,” in which mind is a mysterious non-physical inhabitant of the body. Like Skinner, he thought that such notions should be eliminated in favour of behavioural descriptions.
These “behaviourist” views were very influential but they did not provide any answers to the central puzzle of consciousness: how can sensations, moods, experience and thought emanate from matter? Since the 1970s, this has become the hottest endeavour in philosophy, psychology and the neurosciences.
In his A Materialist Theory of the Mind (1968), DM Armstrong argued that mental entities are identical to physical occurrences in the brain. Although there is a great difficulty about how we should understand this identity, all materialists agree that without some kind of physical basis in the brain’s neural activities, there would be no mental phenomena. Mental phenomena fall into two broad categories: (a) “intentional” states such as thoughts and desires; (b) “qualia,” which are the “what it feels like”…