It is often thought that the main defining characteristic of a person is that a person has consciousness, mind or soul. We are all aware of consciousness (our feelings, thoughts and sensations), however it is more difficult to say what consciousness is.
Plato(c. 427-347 BC) thought that what we really are is our soul, and that this soul will survive after death, indeed death is seen as the release of the soul. Plato is thus asserting that soul and body are distinct substances, bodies die, but souls are immortal.
Aristotle (384-322 BC) Thought that the soul and the body are essentially related. The soul is not a separate substance, but an arrangement of stuff, or material substance, of which the body is made. As Aristotle once said, "If an axe had a soul, its soul would be cutting" For Aristotle then individual immortality seems impossible.
Modern philosophy has developed these 2 themes in a number of ways. Stimulated by Descartes, Leibniz suggested that mind and body only appear to interact: in reality there is no relation between the 2 substances, rather God has pre-established a harmony so that our minds and bodies do not fall out of sync. He uses the analogy of the 2 clocks to illustrate his point. God is seen the master craftsman who has created 2 clocks of such perfection that they always show the same time. Whilst this point of view does not rule out immortality, it does seem that free will can not exist as god has pre-established all possible activities.
T.H. Huxley (1825-1895) was an epiphenomenalist. For him the mind is a product of the (material) brain. For example if I think that I want some chocolate, this may be because my stomach is sending messages to the brain because my blood sugar level is low. For an epiphenomenalist consciousness has no power to cause anything, it is simply a reflection of biology, and of course when the body dies, the mind dies with it.
Recent philosophers are interested in the possibility of artificial intelligence. For example, a thermostat may be said to have 3 beliefs "It's to hot in here, it's too cold in here" and "the temperature is just right". Could it be that human beings are machines that are just more sophisticated?
Descartes and Dualism
Descartes (1596-1650), the "father of modern philosophy" reopened the debate with his dualistic view.
Rene Descartes (1596-1650) used his famous "method of doubt" to show that he could not doubt the existence of his mind. As doubting involved thought, and thought needs a consciousness to think it, Descartes was sure that he could not doubt his mind existed: cogito ergo sum "I think therefore I am".
He did think that it was possible to doubt the existence of his body. Many times he had dreams, which when he awoke he found to have no basis in reality. He imagined that a malicious demon might be fooling him into believing that he had a body. Later he argues that God exists and that as God exists he can be fairly sure that his body exits also.
He is called a dualist because he thinks that mind and body are separate and distinct substances: Mind is conscious and non-spatial and body is spatial but not conscious. He also thought that these 2 substances interact, via the pineal gland.
Most criticisms of Descartes are based on the impossibly of 2 completely different types of substance interacting: How can a non-spatial thing interact with a spatial thing?
Descartes theory does allow for the immortality of the soul, which is perhaps why it has been so influential.
1) Identity Theory
Spinoza (1632-77) suggested a way out from the problems of dualism. Mind and body are not 2 different substances that interact; rather they are both attributes of one substance.
In the 20th Century, identity theory has again become popular. The current version of the theory is that the mind is the brain and the brain is the mind. Consciousness is the individual's experience of the brain, and a scientist can observe brain processes that correspond to conscious experience.
Think of pain. If you stub your toe, you will be aware of pain. On a physical level, your central nervous system is sending messages from your toe to your brain.
Suppose you want to raise your arm. Your decision to move your body sends messages from your brain to your muscles and your arm moves. It seems that Descartes problem of interaction has been solved: there is only one substance, and as there is only one there is no problem of interaction.
This is fine when talking about pain and simple movements; things get a bit more complex with complex concepts. Say I am thinking of the concept of freedom or of Paris in the springtime, and so are you. Is it likely that either of us have the same physical bits of the brain occupied by this thought, or that a scientist using a brain scanner could read off our thoughts?
The behaviourist approach solves the mind body problem by rejecting the concept of "mind". As science can only deal with the observable, and as the mind is not observable then nothing can be said about it. Psychologists are not denying that we have consciousness, they are simply saying that from a scientific point of view only behaviour can be analysed.
Gilbert Ryle (1900-76) developed this approach. He criticised Descartes view that human beings have a "ghost in the machine" by suggesting that the confusion about mind and body arises by the way we use the word "mind". Ryle says that when we refer to someone as "intelligent" then we are, in fact, making judgements about that person's behaviour, that they acted intelligently on a particular occasion. Intelligence therefore does not refer to some hidden private entity.
The mistake philosophers have made is due to a category mistake. Imagine a visitor to a university. A lecturer is showing the person round: "This is the research area, this is the library, this is the lecture theatre", the visitor then asks "But where is the university" as though the university was another building. Ryle says that our notions of mind are like this: "I can see the person behaving intelligently, or sadly, but where is the mind that is doing this". For Ryle mind is simply a term referring to types of behaviour or dispositions to behave.
There are 2 main problems with this approach. Firstly, for most of us what is interesting about mind or consciousness, is out awareness of it, rather than our behaviour. Secondly, it is not clear that all mental states have corresponding behaviour. What behaviour is associated with hearing a tune, or remembering your 5th birthday? From the point of view of an observer, the behaviour associated with both types of mental activity may appear identical.