TYPE IDENTITY THEORY

This diagram demonstrates property dualism — that the brain exists as a physical substance with both mental properties, such as thoughts and feelings, and physical properties, such as size, shape and chemistry.

I find identity theory keeps expanding rather like the universe after the big bang. Various sources deal with types of identity theories of mind.

Type physicalism (also known as reductive materialism, type identity theory, mind-brain identity theory and identity theory of mind) is a physicalist theory, in philosophy of mind. It asserts that mental events can be grouped into types, and can then be correlated with types of physical events in the brain. For example, one type of mental event like "mental pains" will, presumably, turn out to be describing one type of physical event (like C-fibre firings).

C fibres are found in the nerves of the somatic sensory system. They are afferent fibres, conveying input signals from the periphery to the central nervous system. C fibres are unmyelinated unlike most other fibres in the nervous system. This lack of myelination is the cause of their slow conduction velocity, which is on the order of no more than 2 m/s. C fibres are on average 0.2 - 1.5 µm in diameter.

Type physicalism is contrasted by token identity physicalism. Token identity physicalism argues that mental events are unlikely to have "steady" or categorical biological correlates. These positions make use of the philosophical Type-token distinction (e.g. having the same type of car need not mean that you and your friend share a token, a single vehicle). Type physicalism can now be understood to argue that there is identicalness between types, whereas token identity physicalism says we are only describing a particular, unique, brain event.

And from another source:

Type identity theory, or type physicalism is the theory that brain activity and corresponding mental processes are type-identical. The term type in this version of identity theory is meant to signify a difference between type and token, in which type is a category and token is an instance of a member of that category. For instance, the phrase “bigger and bigger and bigger” contains two types of words (the types being “bigger” and “and”) and five tokens (three tokens of the type “bigger” and two tokens of the type “and”). So, activity in a specific type of tissue or area of the brain may correspond with pleasure, making pleasure and that brain activity type-identical.

Token Physicalism / Token Identity

Token identity from type identity in that the relationship between a physical and mental event is more specific to the event. A specific token of a physical occurrence in the brain corresponds with a specific token of a mental activity. Token identity theory more broadly states that mental and physical processes generally refer to the same thing, though they need not be necessarily of a specific type on either side. Token physicalism is, in essence, the same as property dualism which holds that mental properties of the brain (mental tokens) correspond with physical properties of the brain (physical tokens) — both of which are analogous to each other and refer to the same physical object, but which differ ontologically in that mental processes are of a different quality than their physical counterparts.

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