Mind-Brain Identity theory refers to the view where mental states are physical states of the brain and the central nervous system. So to talk about pain, to talk about anger, to talk about doubt, even to talk about thought, is just to talk about certain states of the brain
On the mind-brain identity theory, anger is identified with those states of the brain that give rise to our overt anger behaviour
There are multiple versions of identity theory, including: type physicalism and token physicalism
Type Physicalism
Type physicalism holds that every type of mental state corresponds to a specific type of physical state, such as equating pain with c-fiber stimulation.
In this view, every species to have a given mental state, it must have the same physical structure or brain state, so every being in pain must have c-fiber firing.
An objection to type physicalism is the Chauvinism objection (See Putnam and Fodor for more) saying that type physicalism is “chauvinistic” or too narrow. We are inclined to show an irrational preference for things that are like us. Type physicalism implies that any being that doesn’t have the brain structure or brain states as the average human being will, by definition, be incapable of having mental states like ours.
For instance, octopuses have different brain structures than us, so type physicalism says that they cannot feel pain like us, which seems irrational.
Example of brain-damaged humans shows that mental functions like memory can sometimes be recovered by different parts of the brain than those originally responsible. This suggests that the same mental state (e.g., remembering) can be realized by different physical brain states. However, type physicalism claims that each mental type must correspond to one specific physical type. So, if memory originally occurred in one brain region, and after recovery occurs in another, the type physicalist would have to say it’s not really memory anymore—since it no longer matches the same physical type, which is absurd.
Token Physicalism
This version of identity theory suggests that there is no type-to-type map of mental states and brain states. It tries to address the chauvinist objection by telling us that a particular kind of mental state can be realized, or, that is, actualized in various ways by various physical systems.
Every particular instance (token) of a mental event is identical to some particular instance (token) of a physical event — but there’s no requirement that the same mental type always corresponds to the same physical type.
- My pain right now = this specific brain event
- your pain might be a different physical event
Analogy = Different keys can open the same kind of lock — not identical keys, but each performs the same function.
This view handles multiple realizability = the mental type (e.g. pain) can be realized by different tokens in different species
Token physicalism leads to Functionalism which focuses less on physical composition and more on the role/function that a state plays