The mind-body problem is the problem of determining the relationship between the human body and the human mind. Philosophical positions on this question are generally predicated on either a reduction of one to the other, or a belief in the discrete coexistence of both.
If the mind is not seen as a "mysterious" substance, and it is assumed there are only mental events and that "the mind" is no more than a series of mental events, then it is possible to inquire about the relation between mind and body in terms of the relation between mental events and physical events . One can ask: are mental events completely different from physical events, so that you can't explain what mental events are in terms of physical events; or are mental events somehow explainable as being identical with certain physical events? For example, when John feels a pain, a mental event is occurring; is that pain identical to something that is physically occurring in John's brain, such as the firing of some special group of neurons?
The mind-body problem can be introduced more fully with the following example. Suppose John decides to walk across the room, whereupon he does in fact walk across the room. John's decision is a mental event and his walking across the room is a physical event. In addition, there is another physical event involved, namely, something occurs in John's brain that tells John's legs to start walking. This brain event is closely connected with John's decision; the brain event happens at about the same time, or right after, John decides to walk across the room. One might ask: how is it possible that a decision, a mental event, results in something physical happening in John's brain? If it is claimed that the mental and the physical are completely different, then how can one have any causal impact on the other? How can a mere mental event, a decision, actually cause neurons in one's brain to start firing?
A different philosophical view describes the situation thus: John's decision is itself a physical event. When John decides to take a walk across the room, a group of neurons fire in his brain. He is not aware of those neurons; but the firing of those neurons is itself just the same as his decision. There isn't any more to the decision than that physical event. In this view there's no trouble thinking about how a mental event can have a physical effect; mental events are themselves physical. Ultimately, everything is physical.
To many it may sound strange to say that a mental process is no more than a special kind of physical process. Many believe the mind is more spiritual, ethereal, and is simply not the sort of thing that can be physical. Still, there are other reasons for rejecting this reduction of the mental to the physical.
In the past, some philosophers have believed instead that the reduction goes the other way, that the body should be explained in terms of mental events. In this way, the physical is reduced to the mental. In this view, when John walks across the room, really that was only happening in John's mind and perhaps also in each of our minds individually at the same time. There is, in this view, nothing more to John's walking across the room than our having the thought, or the perception, that it happens. This view would also solve the problem of how the mental can affect the physical. Since physical events are themselves nothing more than a special kind of mental event, then of course there is no trouble about how a decision, which is obviously a mental event, can result in our bodies moving, which is also a mental event, although less obviously so.
The three above-described views about the relationship between the mental and the physical have names:
- Dualism is the view that mental events and physical events are totally different kinds of events.
- Materialism, or physicalism, is the view that mental events are nothing more than a special kind of physical event.
Materialism and Phenomenalism are two opposite forms of monism since they both assume that only a kind of substance (respectively, matter or mind) exists.
The mind-body problem, to put it as generically and broadly as possible, is this question: "What is the basic relationship between the mental and the physical?" For the sake of simplicity, we can state the problem in terms of mental and physical events. It could just as well be put in terms of processes, or of consciousness. So the problem restated is: "What is the basic relationship between mental events and physical events?"
There are, then, three basic views: mental and physical events are totally different, and cannot be reduced to each other (dualism); mental events are to be reduced to physical events (materialism); and physical events are to be reduced to mental events (phenomenalism). To put it in terms of what exists "ultimately", we could say that according to dualism, both mental and physical events exist ultimately; according to materialism, only physical events exist ultimately; and according to phenomenalism, only mental events exist ultimately. Materialism and phenomenalism are both varieties of monism, and of monism there is one further variety, namely neutral monism.
What science has to say
Most neuroscientists believe in the identity of mind and brain, a position that may be considered related to materialism and physicalism, though there is a subtle difference; namely, that postulating an identity between mind and brain (or more specifically, particular types of neuronal interactions) does not necessarily imply that mental events are 'nothing more' than physical events, but rather is more akin to saying that physical events and mental events are different aspects of a more fundamental mental-physical substratum which can be perceived as both mental and physical, depending on perspective
Since most neuroscientists believe in the identity of mind and brain, it may not be surprising to hear that the search for the neural correlate of consciousness (NCC) has become something of a Holy Grail in the neuroscientific community.
A major shift in the neurosciences occurred in the 1990s: the topic of consciousness and its relation to brain function has become a respectable topic that many neuroscientists take seriously. Prior to the 1990s, few neuroscientists spoke of consciousness, and even fewer would be bold enough to try to approach the topic scientifically. Consciousness was not considered to be a topic that was amenable to the methods of science. The tide change in the neuroscientific community of the 1990s is largely due to outspoken scientists such as Nobel-laureate Francis Crick, and philosophers such as David Chalmers. While neuroscience has not yet solved the mind-brain problem in terms of coming up with an NCC, to many in the field, the next decade looks promising. Future research may soon reveal how far science can go in addressing and solving the question of the mind-brain problem.