The variety of activities called 'thinking' is extremely large but includes at least: reflecting, anticipating, deciding, imagining, remembering, wondering, pondering, intending, believing' , disbelieving, meditating, understanding, inferring, predicting and introspecting.
Thinking may take place in language, in an ordinary language such as English, or in an artificial language such as a logical notation. Some thinking also takes place in neither of those media but in mental images - pictures in the mind's eye.
'Thought' is ambiguous between 'what is thought' and 'the thinking of what is thought'. Thoughts may be true or false in the sense that what is thought may be true or false; so, if a person thinks that p, and p is true, then the thought that p is true; and if a person thinks that p, and p is false, then the thought that p is false. Also, there may obtain logical relations between thoughts because, for example, one thought may follow logically from another and contradict yet another.
All thinking has some subject matter. It does not make sense to say there is thinking that is not about anything. If there is thinking, there is something that is thought, some content, even if the thought is not truth-valued but, say, interrogative or subjunctive.
Thinking may be conscious or unconscious. If thinking is unconscious, then the mind thinking either does not know that it is thinking or, if it does know that, then it does not know what it is thinking. If thinking is conscious, then the thinking mind knows both that it is thinking and what it is thinking. Also, thinking may or may not have a phenomenology. Thinking has a phenomenology if and only if that thinking includes events which are experiences.
Thinking is a completely mental activity. I mean by this that no mental event is identical with any physical event and no mental event has any (intrinsic) physical properties. It logically follows from this that materialism is false because that is the conjunction of 'putatively mental events are physical' with 'only physical events exist'. I hold it to be self-contradictory to affirm that any mental event is a physical event, because mental and physical events are truly characterized by mutually exclusive predicates, for example, every physical event has size and no mental event has size; and it logically follows from those two premisses alone that no mental event is a physical event. It logically follows from that in turn that the first conjunct of materialism is false, because that is the claim that mental events are physical. It also follows that it is false that only physical events exist from the premisses that there exist mental events and that no mental event is identical with any physical event. It logically follows that the second conjunct of materialism is also false.
Materialism is a self-contradictory theory of the mind because it includes the claim that the mental is physical; but being mental partly consists in having no physical properties and being physical partly consists in having no mental properties. Being self-contradictory is a logically sufficient condition for being false, so it follows that materialism is false.
The relation between thinking and the brain is this: thinking is the mental activity of the brain. Crucially, there is no interface problem between things and their activities. There is no ontological or metaphysical problem about what the relation is between something and what it does. It is what I am calling the 'interface problem' that has proved most intractable in solving the mind-body problem: stating the nature of the interface between a mental event and a physical event. Materialists incoherently maintain that mental events are physical. Idealists incoherently maintain that physical events are mental. Dualists correctly maintain that no mental event is physical and that no physical event is mental but falsely believe in the interface problem.
To believe in the interface problem is to be in the grip of a metaphysical illusion, a powerful one which governs our self-conception. To help dispel the illusion, I provide a number of analogies. They are designed to show there is no ontological problem about something and its activities, or about a thing and what it does.
A light-bulb increases and diminishes in brightness, but there is no 'light-bulb-brightness' problem. Note that, were we to break the bulb or cut off the electrical supply, or if the filament were to wear out, the emission of light would cease. In the Lewis Carroll story Alice in Wonderland the speculative metaphysical possibility is imaginatively entertained of a 'grin without a cat'. Clearly, however, in empirical reality there may exist a cat without a grin but not a grin without a cat (or something that grins). This is because grinning is something the cat does. A chameleon is a lizard that can change its colour. Suppose the chameleon changes from blue to red. There is not thereby created a 'chameleon-colour-change problem', not just because secondary qualities logically depend upon primary qualities but also because changes logically depend upon things that change. If a bus is moving down the street, there is no 'bus-motion problem'. It is not as though the motion of the bus could exist as a ghostly see-through residue, were the bus to be dismantled. This is not just because primary qualities logically depend upon the physical objects they are properties of but also because moving is something the bus does and doings are impossible without the things that do them.
Nothing hinges, in any of these cases, on whether the things done are physical or mental or neither. It is because things done logically depend on things that do them that there is no interface problem.
In a similar way there need no longer be a mind-body problem. We, logically, could never be in a position to inspect the 'interface' between thinking and the brain. We could never, so to speak, peel thinking off the brain and discover metaphysical cement, cement that is not quite mental and not quite physical. To believe in the interface problem is to confuse an empirical possibility with a logical impossibility.
I call this solution to the mind-body problem 'Empiricism' even though, as a general thesis about thinking, it is analytic: 'thinking is the mental activity of minds'. As a particular truth about human beings and higher animals, it is empirical and contingent: 'thinking is the mental activity of the brain'. It is an important tenet of this empiricist theory of the mind that little sense may be attached to the metaphysical notion of a 'relation' between a thing and its activities. Something's activities are just what it does, whatever it is and whatever it does. All the facts about a thing's relation to what it does are empirical facts; none of them is metaphysical.
Notably there are no causal relations between things and their activities other
than those to be mentioned in explaining how or why they engage in those
activities. If we persist in thinking of thinking as a thing or substance, we
will continue to ask about causal connections between thinking and the brain,
instead of correctly regarding thinking as the mental activity of the brain. It
is an empirical question, which parts of the brain are required for which kinds
of thinking. There is no non-empirical causal question about thinking and
the brain. It is an empirical truth that the brain is necessary for
thinking in humans and higher animals, and it is an empirical truth that
thinking is an activity, or something that is done. The empiricist theory of
the mind is the identification of the brain with that which engages in the
activity of thinking. This identification is itself empirical.
(THEORIES OF THE MIND, PENGUIN 1991, p. 213-216)
