A swan is a bird and (usually) white, but what makes it a bird (a biological property) and what makes it white (a color property) are different properties, though both are physical properties. So there are lots of different kinds of physical properties. We can ask, are mental properties a kind of physical property? For example, can thinking a thought, holding a belief, or feeling an itch be considered a neurophysiological property? According to Steven Schneider of Harvard University, ‘Type identity theory’ claims that mental properties are just physical properties. If we say that these physical properties are properties of a brain, then the theory is mind–brain type identity theory. So this theory claims that thinking a thought or feeling an itch is exactly the same thing as certain neurons firing and having a belief is the same thing as certain neural connections existing. Any particular type of mental state is a particular type of brain state. (Schneider, n.d)
Mind–brain type identity theory was developed in the 1950’s as neuroscience gathered pace. The evidence is that mental events and states are very closely dependent on the brain, so many people now think that ‘the mind’ is just ‘the brain’, and everything mental is actually neurophysiological. However, this claim needs to be distinguished from the claim that mental states are correlated with brain states. For example, having a heart is correlated with having kidneys, every animal that has a heart has kidneys and vice versa. But hearts and kidneys are not the same thing. Or again, having a size and having a shape are correlated, everything that has a size has a shape and vice versa. But size and shape are distinct properties. So simply pointing out that everything that has a particular brain state also has a particular mental state doesn’t show that mental states and brain states are the same thing. Correlation is not identity.
Neuroscientific evidence can establish correlations between mental and physical properties, but this does not in and of itself establish the type identity theory. Certain materialistic and physicalistic aspects regarding the identity theory don’t claim that mental properties are correlated with certain physical properties. They say they are identical with them. But to demonstrate identity, we need to think philosophically, not scientifically. The theory is called ‘type’ identity, because it claims that mental ‘types’ of thing (mental properties, states and events) are physical ‘types’ of thing, physical properties, states and events. Mental ‘things’ turn out to be the same type of ‘thing’ as physical ‘things’, and so mental properties are actually physical properties of the brain, mental states are brain states. They may not seem the same, but that’s because we have different ways of knowing about these properties, through experience and through neuroscience. Many things turn out to be something they don’t seem to be, e.g. solid objects are mostly empty space, water is just hydrogen and oxygen.
Type identity theory is a form of ‘reduction’. The word reduction has a bewildering range of applications in literature. Patricia Churchland, an analytical philosopher noted for her contributions to neurophilosophy and the philosophy of mind, explains how reduction is first and foremost a relation between theories. Most simply, one theory, the reduced theory, stands in a certain relation to another more basic theory. (Churchland, 1990) An ontological reduction holds the idea that the things in one domain (mental things) are identical with some of the things in another domain (physical things). For example, we can argue that heat is just mean molecular kinetic energy. They are the same thing. There is nothing more to mental properties than being a certain kind of physical property.
Mind-brain identity theory contrasts with long-held beliefs attributed to Rene Descartes, a seventeenth-century French philosopher, mathematician and scientist who is considered the father of modern Western philosophy. The ideas put forth by Descartes and other philosophers over the past three centuries assert that the mind is both immaterial and non-physical. In fact, the mind-brain identity theory stands in contrast to all other philosophies in the category of mind-body dualism, which contends that the mind and body are distinct and different substances. Alexander Moreira-Almeida, a Brazilian psychiatrist, describes the dangers of dualism and it’s credibility in neuropsychiatry.
“Based on the assumption that mind-brain dualism does not allow mind-brain interactions, dualism was presented as a major block to neuropsychiatry and to an integrative or biopsychosocial understanding of patients, mental disorders, and their treatments.” (Moreira-Almeida, 2018)
Both substance dualism (mind and brain are different substances) and logical behaviorism face difficulties explaining mental causation. On the one hand, if minds and bodies are distinct, it is hard to see how events in one could cause events in the other. On the other hand, we do not want to deny, that there is any mental causation. Type identity theory claims to solve the problem. All mental properties are identical with brain properties. Mental occurrences are identical with neurons firing. Mental states that involve behavioral dispositions are neurological connections. And so all mental causation just becomes a form of physical causation. For my desire for food to cause my searching for food is just for certain physical properties of my brain to cause that behavior. Mental states and processes cause actions because they are physical states and processes.
There is one thing identity theory still has little to say on, however, and that is: what is it to have a particular conscious experience? To answer what it is to be in pain, an identity theorist might look up you in a table and find the corresponding physical properties of the brain, and tell you that to be in pain is to have a particular physiological state. But does that tell us all there is to know about pain? It somehow seems unsatisfactory. British philosopher and psychologist U.T. Place, one of the developers of the identity theory of mind, wrote in his 1954 paper "Is Consciousness a Brain Process?" this assertion on the topic:
"The view that there exists a separate class of events, mental events, that cannot be described in terms of the concepts employed by the physical sciences no longer commands the universal and unquestioning acceptance among philosophers and psychologists that it once did." (Place, 1956)
Place answered the question ‘Is Consciousness a Brain Process?’ in the affirmative. But what sort of brain process? There is a challenge to the identity theorist to dispel this feeling.
To explain this idea, imagine someone jogging to the park. They could have crossed a street, gone along a twisting road for half a mile, avoided oncoming traffic, and yet have no memories of all this. In one way, they were conscious. They were perceiving, gathering information about position and speed, the movement of approaching cars, the length of a familiar path. However, in another way, they were not conscious. They were on ‘automatic pilot’. Try to use the word ‘awareness’ for this automatic or subconscious sort of consciousness. Edward N. Zalta, a senior research scholar at the Center for the Study of Language and Information, compared consciousness with proprioception. A case of proprioception occurs when the eyes shut and, without touch, there is an immediate awareness of the angle at which an elbow is bent. That is, proprioception is a special sense, different from that of bodily sensation, in which there is an awareness of parts the body. (Zalta, 2017) Now the brain is part of the body, and so perhaps immediate awareness of a process in, or a state of, the brain may here for present purposes be called ‘proprioception’. Thus the proprioception even though the neuroanatomy is different. Thus the proprioception which constitutes consciousness, as distinguished from mere awareness, is a higher order awareness, a perception of one part of, or configuration in, the brain by the brain itself. Some may sense circularity here. If so, let them suppose that the proprioception occurs in an in practice negligible time after the process propriocepted. Then perhaps there can be proprioceptions of proprioceptions, proprioceptions of proprioceptions of proprioceptions, and so on up. The last proprioception in the sequence will not be propriocepted, and this may help to explain a sense of the ineffability of consciousness Place argues.
Now, given the status of the current knowledge and the absence of a truly complete theory of the Mind-Body Problem (the problem of whether these theories are just that), the best way to achieve progress is to recognize that the MBP is far from being solved and to be open to competing theoretical models, as is being done in contemporary physics and philosophy of mind. It is crucial that several models of the MBP be allowed to develop and show their value, or lack thereof. Rather than misrepresenting potential candidates, it is more productive to consider alternative hypotheses seriously and test them rigorously with respect for what they propose.