The Identity Theory of Mind
Introduction
What is the nature of the mind? According to the theory called “dualism” the mind a is non physical something or other which inhabits our bodies (specifically our heads). Thus a person is composed of a physical body and a non physical mind - hence “dualism”. If dualism is true then the human mind is essentially mysterious and forever beyond the understanding of physical science. Yet neuroscience has discovered a lot about the workings of the mind, especially over the last few decades. A lot has been discovered about the chemistry of the brain - neurotransmitters, etc, about its anatomy and physiology. Not only that, but there has been considerable progress towards understanding the physical basis of mental abilities such as memory, the recognition of faces, language learning and so on. If the mind is indeed beyond the scope of science, there is not much sign of that at the moment. Dualism seems an implausible and defeatist view. Is there a better one? One alternative to dualism is the identity theory of the mind.What is the identity theory?
The identity theory is a physicalist theory of the mind. Physicalist theories of the mind assert that the mind is physical and that human beings are therefore complex physical organisms. There are no non-physical minds, spirits or souls. But what does “physical” mean exactly? Without actually defining “physical” we can say that something is physical if it has most, but not necessarily all, of the following properties: shape, size, position, duration, mass, charge, atomic structure, temperature.The identity theory is usually stated in terms of mental events or states. Examples of these are deciding to go to the movies, seeing the light go red, feeling a sudden toothache, having a nightmare, wanting an icecream, thinking about the exams, being in love and knowing that Dubbo is in NSW. The identity theory can be stated as follows:
Every mental event is identical with some physical event, specifically some event in the brain.
Identity statements like this occur frequently in science and they provide the model for the identity theory. For example, water = H20, lightning = electrical discharge, temperature = mean molecular kinetic energy, cloud = collection of water droplets in suspension. These identity statements are examples of what is called “reduction”. To say that lightning = electrical discharge is to “reduce” lightning to electrical discharge. This is often expressed by saying that lightning is nothing but electrical discharge. Where we might have thought that there were two things, lightning and electrical discharge, in fact there is only one - electrical discharge. The point is not that lightning doesn't exist. The flashes which we see do really exist. The point is that we now have at our disposal a scientific theory which can explain why those flashes occur. Where we previously might have been inclined to think (and for centuries probably did think) that the flashes in the sky were quite separate from anything else that we know about or understand, science has shown that this is not so. Those flashes are just good old electrical discharge that we are familiar with from such things as spark plugs. As mentioned earlier, science has shown that those flashes in the sky are not entities which exist in addition to the basic entities of science, specifically electrical discharge. Yet lightning is not like, say, being “possessed by the devil”. There is no such thing as demonic possession. To explain the condition described as “demonic possession” as, say, paranoid schizophrenia is not to say that demonic possession=paranoid schizophrenia. Science has not reduced the notion of demonic possession to that of paranoiac schizophrenia. Science has shown that there is no such thing as demonic possession. That is where lightning, water, clouds and temperature are different. We were not as radically mistaken about lightning, water, etc as we were about demonic possession or phlogiston. Science has given us a deeper insight into the nature of lightning, water, clouds and temperature by reducing these notions to more basic notions like molecules, electricity and so on. And the aim of reduction is to offer explanations which are as simple as possible - use as few different types of entity as possible. To illustrate, the planet Venus was in the past referred to both as the “morning star” and the “evening star”, before it was realised that in fact the morning star = the evening star. There were not two things, morning star and evening star, as previously thought but only one, the planet Venus.
The identity theory of the mind, then, is a reductive theory. The aim is to reduce the notion of the mind to more basic and better understood notions such as neuron firings, stimulation of c-fibres, neurotransmitters and so on. In other words, it is an attempt to do for the notion of the mind what has already been done for lightning, water, clouds and temperature. The identity theory asserts that all our mental states and events can eventually be placed in one to one correspondence with certain states and events in the brain. So that's what the identity theory is, but why believe it? What are the arguments in support of the identity theory?
Arguments for the identity theory
- Success of neurosciences: Neuroscience is the science of the brain, and includes neuroanatomy, neurochemistry and neurophysiology. Just as there has been considerable success in explaining the behaviour of simple creatures like sea slugs in terms of the detailed workings of their central nervous systems, so too has there been considerable success in explaining many aspects of human behaviour in terms of the structures and chemistry of the brain. As mentioned earlier, this has involved those specific parts of the brain responsible for language, the emotions, memory, reading, recognising faces, seeing, hearing, pathological conditions such as schizophrenia and epilepsy, and so on. Thus identity theorists argue that eventually it will be possible to locate precisely those events in the brain which are associated with all types of mental event - thoughts, decisions, beliefs, pains, dreams, desires and the rest.
- Simplicity: Mental and physical events are causally interdependent. Stepping on a nail causes pain and substances such as alcohol and narcotics affect our thoughts and emotions. Also, in the opposite direction, seeing the traffic lights change can cause you to put your foot on the brake. If mental events are identical with physical events (in the brain), then these dependencies between mental and physical are just what would be expected. Furthermore, the identity theory is preferable on grounds of simplicity. Why not settle only for the existence of neural events rather than for both neural and mental events? The identity theory simplifies our view of the world, as does the electrical discharge theory of lightning.
Arguments against the Identity Theory
- The Leibniz Law problem: Leibniz's law states that if x = y then everything true of x must also be true of y. For example, if Clark Kent = Superman, and Superman loves Lois, then it must be true that Clark loves Lois. The problem for the identity theory is this: Suppose, for example, that it were established that deciding to do X = brain event of type D. Now, decisions can be wise, hasty, stupid, difficult and so on. Therefore according to Leibniz's law, brain events of type D can be wise, hasty, stupid or difficult. Yet these terms don't seem to make any sense when applied to events in the brain. Brain events can, for example, last for 4.2 milliseconds or can occur in the cortex, but what does it mean to say that a brain event is wise or hasty? So it seems that mental events cannot be identical with physical events in the brain.
Question: Before it was established that sound is a wave phenomenon, did it make sense to talk about the wavelength of sound?
- Qualia: The term “qualia” stands for those qualities of our experience such as bitterness, sweetness or sourness of tastes, or the stinging, burning or throbbing of pains, and so on. The identity theory, it is claimed, only gives a scientific account of the mind in terms of neuron firings and neurotransmitters and the like, but can't describe the character of our experience. In other words, it can't account for qualia and is therefore incomplete. To illustrate the point, imagine a future neurophysiologist Mary who has a complete knowledge of the brain mechanisms underlying pain. Unfortunately Mary is one of that small number of people who are congenitally insensitive to pain. Then, although Mary knows all about the physical mechanisms of pain she doesn't know what it's actually like to be in pain. Her scientific knowledge, comprehensive as it may be, is fundamentally incomplete because it leaves out the qualia of pain. Mary's knowledge of physical mechanisms simply doesn't amount to knowledge of what it is like to feel pain. So the identity theory is incomplete and is therefore an inadequate theory of the mind.
Question: The case of Mary is based on there being two ways of knowing about pain - directly through experience (which Mary couldn't do), and indirectly by way of neuroscience (which Mary could do). Does the existence of two ways of knowing imply that what is known is different in each case? Compare: If you have the “evening view” of Venus, then for you it's the evening star. If you have the “morning view” of Venus, then for you it's the morning star. Though it may be that the evening view is different from the morning view, it turns out that each view is of the same thing, namely Venus.
- The mental states of aliens: ET, you remember, wanted to phone home. Suppose, as is likely, that ET's physical constitution is quite different from ours. Then it seems to make sense to attribute desires to alien beings even if their physical makeup is quite different from ours - they might be silicon based rather than carbon based. But if a silicon based being could have mental states such as desires, thoughts and beliefs, then these mental states can't be identical with states of the brain as asserted by the identity theory. In other words, it seems that the physical constitution of a mental state - out of neural patternings, for example - is not what is essential to being a mental state.
Questions: If physical constitution (out of brain states) is not essential to being a mental state, then what is? Was it the aim of the identity theory to give the “essence” of being a mental state?