7.2: The Brain State Identity Theory

Ryle’s behaviorism attempts to make talk of mental states empirically respectable by defining mental terms in terms of observable conditions and behaviors. One concern raised about this approach was that mental state terms are to be understood entirely in terms of observable things going on outside the person. This seems to take the mind out of the person. There is no place in behaviorism for any account of our inner lives or even the notion that my beliefs and desires are in some sense in me or part of me. The Brain State Identity Theory, most ably advanced by J. J. C. Smart, goes some ways towards remedying this apparent defect (though Ryle would not have counted it as a defect). The Brain State Identity Theory proposes that mental states are identical with brain states. Contrary to Descartes’ dualism, the Identity Theory takes mind to be a physical thing. Namely, it takes the mind to be identical with the brain. For this reason, we count the Identity Theory as a physicalist view of the mind.

According to the Identity theory, the belief that Obama was president of the USA in 2002 just is a certain neuro-chemical state of the brain. Note that a great many people share this belief. When we speak of the belief as a view about what is true, one that might be shared by many people, we are speaking of a belief type. My belief that Obama was the American president in 2002 is just one token of that shared belief type. This distinction between types and tokens is important to understanding what the identity theory says. The Identity Theory originally proposed that mental state types are identical with brain state types. So for you to have the mental property of believing that Obama was president of the USA in 2002 is just for your brain to have a certain specific neuro-chemical property. The identity theory holds that for anyone to have the belief that Obama was president in 2002 is just for them to have that same specific neuro-chemical property. A popular and plausible example of such mental state/brain state type identity was that pain just is C-fibers, a certain kind of neuron, firing.

We have scientific evidence that very roughly points in the direction for something like the Identity Theory. Cases of localized brain injuries indicate that different parts of the brain carry out different functions. People who suffer lesions in specific areas of the brain tend to find specific mental functions impaired while other functions are left perfectly intact. It is through analyzing such cases that we began to map areas of the brain according to the functions they perform.

In the Identity Theory we witness a significant point of intersection between the philosophy of mind and the science of mind. Philosophical speculation has given rise to a great many scientific hypotheses. Here we have an example of how this can happen. We have a theory about the metaphysical nature of mental states that turns out to be empirically testable. The Identity Theory says that mental state types are identical with brain state types. Types are properties, so this view tells us that all of your mental properties are physical properties of your brain. We have learned a great deal about how brains store and process information since this hypothesis was popular. The science of mind is not yet mature, but well past its infancy and the broad outlines of how brains work are more or less in place. What the science tells us is that different brains store and process the same information in very different ways. That is, the Identity Theory is wrong. My belief that Obama was president in 2002 involves many properties of my brain. But your belief that Obama was president in 2002 involves your brain having different properties.