Theories about mind can be divided into two distinct varieties. One the one hand there are monist theories which claim that the world consists of one kind stuff or substance. On the other hand their are dualist theories which claim that world consists of two substances: typically the mental and the physical. Monism the theory that the world consists of one fundamental substance comes in four distinct varieties each of which I will briefly outline.
Four Distinct Varieties of Monism
- Idealism or Solipsism, is the idea that the world is completely mental. Idealism claims that there is only one thing to our ontology, namely ideas. Idealism however suffers from a couple of serious problems. Firstly, Idealism seems to have problems in accounting for the persistence of objects. It seems that Idealist is going to struggle to explain how objects persist during periods of time when they are unperceived. Secondly, experience appears to involuntary, what we experience appears to be caused by something beyond ourselves (a physical world perhaps?). Historically Berkeley is the best known proponent of Idealism and sought to avoid some of the apparent problems of Idealism by bringing God into the picture. The Solipsist extends this and claims that the whole of existence is constituted by their Ideas, everything is taken to be an Idea within their own mind.
- Physicalism: the physicalist makes the claim that there is only one kind of stuff and that stuff is of the physical kind. The Physicalist project requires that everything must at least be explained or reduced to the physical. Typically this has led physicalists to reduce mental properties and events to brain states or properties of the physical brain. For example a physicalist may claim that being in pain will ultimately be shown to be nothing more than being in a particular relevant brain state.
- Neutral Monism holds that reality is neither mental or physical as we understand the terms but really consists of one kind other stuff perhaps encompassing both the mental and the physical.
- Mental and Physical Monism, reality is essentially a single substance, but at the same time is both mental and physical. This leads to a kind of Panpsychism where the fundamental building blocks of the universe are to be taken both experiential and physical. Adopting such a position could lead us to hold that inanimate objects such as rocks may have some kind of conscious experience. One example of a prominent modern panpsychist would be the University of Reading's Galen Strawson.
The major alternative to the forms of Monism is to adopt Dualism. The best known form of Dualism is substance dualism also commonly known as Cartesian Dualism due to the fact it originates in the work of the French Philosopher Rene Descartes. It this Substance Dualism that the rest of this post will most prominently focus on due to it's significant influence and historical importance. However it is important to note that their are other forms of Dualism. Substance or Cartesian Dualism isn't the only Dualist show in town.
Unsurprisingly, Cartesian Dualism posits two different kinds of substance material bodies and thinking things. Descartes held that there is real distinction between minds and bodies, he felt that they were fundamentally different kinds of thing. Descartes differentiated between Res Cogitans- a thinking and Res Extensa an extended physical thing. What constitutes a person is a matter of res cogitans not Res Extensa. Descartes offers up two different arguments to this effect, the argument from doubt and the argument from clear and distinct ideas.
Generally considered fallacious but still nonetheless one of the best known Philosophical arguments the argument from doubt can be found in both Descartes Discourse and Meditations. The argument is outlined in the Discourse as such:
'I can doubt I have a body. But I cannot doubt that I exist.
Therefore I am not my body.
(Discourse, section IV)
It should be clear to many that this argument is hardly satisfactory. The argument is often taken to be fallacious due to the fact that the move from 'I cannot notice anything except X' to there is 'Nothing but X'. Similarly the argument can be seen fallacious as it also seems to make the invalid move from 'If it isn't known that X belongs to A' then X must not be essential to A. It is often said that the argument introduces extra premises that are not explicitly laid out by Descartes. It seems clear to me that the argument lacks proper logical vigor though it does seem to have a intuitive appeal.
The Argument from Distinct and Clear Ideas
Even if we reject the argument from doubt outright we still have to examine Descartes other argument for Dualism. This argument finds its clearest rendition within Descartes Meditations on First Philosophy.
I have a clear and distinct idea of myself as a thinking, non-extended thing, thus separate from my body. The fact that I can clearly and distinctly understand one thing apart from another is enough to make me certain that the two things are distinct as they are capable of being separated, at least by God (Meditation VI)
Though this argument appears to be no better than the first argument offered by Descartes for the real distinction between the mind and body. The classic counter example offered against the argument from distinct and clear ideas is that it is possible to clearly and distinctly perceive a triangle which happens to be right-angled without clearly and distinctly perceiving that is a Pythagorean triangle. So why think that Descartes argument can show us that I can exist without any physical properties? Descartes answer to this problem was to deny the parallel claiming that what he meant as conceivability as a complete substance and this is clearly not the case in the fora-mentioned example. But this unfortunately doesn't save Descartes argument, as something be can be conceivable without it being possible.
Objections to the Distinction made by Descartes
Prominent modern philosopher of mind, Colin McGinn has rejected the idea that is possible to conceive of an immaterial substance. He maintains that to conceive or think of a substance is simply to think of something that has certain material properties. Whether McGinn is correct seems somewhat questionable in my eyes, but even if the idea of a mental substance without material properties is conceivable it does seem terribly problematic. For example it seems that an immaterial substance must have properties over and beyond just mental states. Otherwise we appear to arrive at the truism that mental states are mental states. Pinning down what a non mental and non physical property could be like seems near impossible.
The Real Knock Down Objection to Dualism :Causalition?
The problem of how exactly the mental and the physical are meant to causally interact is often taken as the knock down objection against those who hold a form of Substance Dualism. Descartes wanted to hold that the mental and physical do interact and held that the pineal gland was the point at which the interaction supposedly happened. It seems difficult to hold that two completely separate and different substances could causally interact with one another. This lead to many of Descartes followers to adopt a kind occasionalism, which often leads to the occasionalist to posit God in order to ensure that the mental and physical coexist alongside each other in harmony. The only understanding of causation we have is derived from the physical realm and the principle of causal closure of physics seems pretty well confirmed.
The Merits of Descartes View
Even with all of this being said Dualism remains an attractive proposition to many people. My personal experience seems to suggest that those of a religious disposition are often more inclined to accept dualism, but it does seem that their are some atheists who are also inclined towards accepting such a position. The two points where substance Dualism really seems to excel is that it offers us an account of mind which seems to fit well with our pre-theoretical beliefs. I.e that we have a mind and body which are separate entities. While also avoids the problem of the apparent explanatory gap between talk of the physical world and the mental. Though it should be noted that substance dualism generally considered an untenable position with it find very few supporters among academic philosophers.