Dualism, the philosophical theory that states that there are two kinds of substance: mental and physical, is now largely discredited by the worlds leading philosophers.
It first came to prominence through Ren¯¿½ Descartes in his Meditations as he tried to come to terms with the fact that most of his knowledge was either false or that he did not have enough evidence to believe in it firmly enough. For many centuries the idea was debated and reclassified, changing slightly from philosopher to philosopher and being totally rejected by others. The alternative to dualism is monism, the idea that mental and physical substances are one and the same; that is that the mind is or is contained within (in the tissue of), the brain.
At first it appeared that dualism was indeed a logical conception, as features of the mind and the body seemed very different indeed. Descartes pointed out that while one could imagine oneself without physical features, it was impossible to imagine oneself without a mind; indeed the very action of attempting this was enough to prove that a mind was present. This was the basis of Descartes theory to draw out basic knowledge that he could not be deceived about. Due to this distinction it seemed logical to conclude, using Leibnizs Law, that physical and mental entities were indeed separate. However, Descartes had made a mistake in assuming that his clear and distinct perceptions of a thing made that thing possible.
For example, I can clearly and distinctly conceive of a unicorn, but that does not mean that they exist. (Lewis Carroll parodied this in Through the Looking Glass, in which the Red Queen tells Alice she imagines several impossible things before breakfast. Presumably she has a clear and distinct perception of these things, as when Alice attempts it, she is told she is not trying hard enough.) Also, I can just as clearly perceive of something not being as of it being, and as something cannot both be and not be, it would seem that this theory for basing something upon an unalterable internal proposition falls down. So, the argument from clear and distinct perception cannot be used here as it is just as easy to conceive of the mind and body being separate as it is for them to be one and the same.
There are many scientific and logical arguments in favour of monism, Occams Razor, for example, a theory which asks us to take the simpler solution to a problem over the more complicated theory. For example, before the biology of animals was worked out scientifically, it was believed that all living creatures had an attribute called vitalism, which kept it alive. Now we know the biology, we can use this much simpler explanation. Here it can be applied easily: obviously it is simpler to believe in one substance than two, one of which does not conform to the laws of physics.
There is also scientific evidence that shows us how damaging or experimenting with the brain, which is undeniably physical, can affect a persons mental behaviour. Performing a lobotomy, for instance, can totally alter a persons personality turning them from being calm and rational to being crude and rash, or vice versa. Similarly, stimulating neurons on the Thingybob Strip, which crosses the top of the brain, can cause sensations all over the body. It may be that prodding a part of this strip can make your elbow tingle in a most delightful manner or make your thumb feel as if it is being dragged through warm treacle. It would seem from this that the these feelings are to be found in the prodded part of the brain and this is where the mental is to be found within the physical.
These reasons show that monism is probably the more scientifically favourable position, but are there any reasons that can show Dualism to be the more logical choice? Leibnizs Law might argue for dualism in that there being differences between the physical and the mental, they must therefore be separate substances.
For example, having a chunk of the physical removed does not mean a part of the mental has also been removed. In fact, an awful lot of the physical body can be harmed, even in the brain, before there is a definite mental side effect. Surely, say the dualists, if the some parts of the mental were contained within certain parts of the brain, for example, if the capacity to taste lentils were located solely in a small part of the brain, and that part were to be removed we would no longer have the capacity to taste lentils. But a lot of the brain can be removed, and so, if there were set areas we would be removing certain abilities of the mental. Therefore, the mental must be separate from the physical.
However, it is true that removing some areas of the brain will prevent the mental from performing certain capabilities. It is possible to find out which areas of the brain are functioning when fuelled by particular stimuli, and if, when doing this we slice out those areas of the brain, in some (but not all) cases, those functions will no longer be possible. Also, the left side of the brain and the right side provide vastly different functions one being more practical and other being more intellectual. This would seem to back up the monist theory that the mind is located within certain parts of the brain.
Another counter argument to Dualism could be contained within Feigls concept of Nomological Danglers. If the mental is indeed distinct from the physical it cannot be present within the same world as the physical things we know of, as removing physicals things would inevitably reveal the mental substance. Therefore it follows that it is connected to this physical world in some other way. However, Feigl tells us that it is ridiculous to believe that there is a separate type of law for these substances, which allows them to exist dependently of the rest of physics. Surely the mental substances cannot be dangling outside of the realms of reality?
These masses of arguments for monism overwhelm the poorer, outdated arguments for dualism, which stem from a less scientifically advanced age, in which the solutions appeared to work logically, based on a more internal philosophy of contemplation, which is now being replaced by a more practical philosophy, backed up by the sciences.
Hence it is not unfair to say that previous ideas that worked in favour of dualism are no longer good reasons to believe the theory and that as we have better reasons to take the theory of monism seriously, we must subscribe to it, and not dualism, as the correct theory.