So, let's back up a little bit and think about the more general question about the nature of the mind and its relation to the body. One question is this. Could thinking, feeling, sensing, and the like, be purely physical processes in the way the metabolizing and digesting and sweating seem to be purely physical processes? Well, the answer is no. If thinking, feeling, sensing et cetera are not purely physical processes, you might ask, how can these mental events bring about physical changes in the world? How can physical changes bring about mental events? Sometimes it seems like I can make a decision to raise my hand and whoop! There goes my hand. It goes up. Other cases are ones in which something sharp slices against my leg and I feel an experience of pain. In the first case, we've got a mental event bringing about a physical event. In the second case, we've got a physical event bringing about a mental event. But how can those things happen if mental events are not physical processes at all? On the other hand, if thinking, feeling, sensing, and the like are purely physical processes, how can we make sense of the possibility that many of us just acknowledged of surviving the destruction of my body? How could a purely physical theory makes sense in idea that I could persist after my body is wholly destroyed? This is sometimes referred to as the mind-body problem. What kind of thing is a mind? Is it a purely physical or a non-physical thing? Either answer, it seems like it's going to raise some difficulties. But let's try to get a better sense of where Descarte is coming from. One background assumption that he wants you to make, that seems pretty reasonable, is what's known as the indiscernibility of identicals. It's simple, it goes as follows. If X and Y are identical, Sam Clemens and Mark Twain or the morning star and the evening star or three squared and the number nine, those are all cases of identities. If X and Y are identical, then any property that X has, Y has as well and vice versa. So, if for example Venus is the same thing as the morning star and Venus the planet has a certain mass then the morning star, that same planet has that same mass as well and vice versa. Don't confuse the indiscernibility of identicals with the identity of indiscernibles, which is a different, distinct, non-equivalent and much more controversial claim in philosophy. So, the indiscernibility of identicals. Likewise, I want you to think about the notion of a modal property. In addition to properties like being rectangular, or weighing 43 kilos, being made of sodium, we're also familiar with properties like, being capable of running a mile in eight minutes, being capable of eating five pizzas in one hour. Those are what we refer to as modal properties which you can have even if you're not eating anything, you're not running it right now, you're sitting on the couch relaxing perhaps. But you still have the modal property of being able to do perhaps one of those things. Now here's an argument. Descarte would hope that you'll find each of these premises self-evident. That is, so obvious as to not be worth denying and then he's going to try to convince you of the conclusion as something that just follows logically from the premises. Premise one. I clearly and distinctly perceive the following possibility, that I could exist without my body. And as I suggested many of you probably accepted that already and clearly think perception just involves imagining the possibility, thinking it through carefully, not seeing any internal contradiction or incoherence in it. It's not clear what that would be in the case of disembodied existence and then say, "Okay. So, it seems like that's something I clearly and distinctly perceive as being possible." But if that is possible then it seems like it's also the case that i could exist without my body. So [inaudible] as my mind has the modal property being capable of existing without my body. But notice my body does not have the property being capable of existing without my body. But imagine body and mind are X and Y. We've got X having a certain modal property that Y does not have. Therefore X and Y can't be identical. Because if they were identical, they would have to have all the same properties by the indiscernibility of identicals. Therefore Descarte will confer that my mind and body are distinct. And notice that this argument can be reformulated to refer not just to your body in a gross sense of everything except through your central nervous system. It can be reformulated to even include your central nervous system. In fact, it can be reformulated to refer to any physical substance at all. So, this argument is a sound argument. It is going to show that your mind is not identical with anything physical. Be it your whole body including your central nervous system or your central nervous system detachment body or your cerebral cortex or your prefrontal cortex or any part of your brain. Nothing there'll be identical with your mind. Many people refer to the conclusion of what's now called the body detachment argument as showing that mind and body are distinct. But that's too weak. Because after all my left hand and my right hand are distinct. But that's not going to give me any conclusion about somehow the physical world not being a complete, not containing everything that exists. If Descarte is right, the physical world does not contain everything that exists. There exists things that go beyond the physical, namely minds. But that's a more radical claim than just the claim that mind and body are distinct. Better formulation of this dualistic picture is one according to which my mind is not identical with anything physical. It's distinct in that very dramatic sense. Notice also that although Descartes formulation of this so-called body attachment argument depends upon the theistic premise that refers to clear and distinct perception, we can reformulate it in modern terms that don't require theism, don't require Descartes particular take on the problem of evil in the following way. Premise one. It's possible for me to exist without my body. Many of you probably know so that that is true. Two. I could therefore, that I got the modal property of being capable of existing without my body. My mind then says that modal property. My body does not have it. Therefore, once again mind and body are distinct. So that, my mind is not even from this non-theistic formulation of the argument, we get the conclusion that my mind is not identical with any physical substance whatsoever. And that is a radical conclusion and notice also that it's a conclusion that follows from pretty uncontroversial premises and not very many of them. We're going to see that many subsequent philosophers denied the dualistic inclusion, denied that mind is distinct from the body, asserted something more like a materialistic claim that everything including the mind is a purely physical process or material object without explaining where Descartes's argument goes wrong. Without explaining what the fallacy if any is in it. It's only when we can find out where Descartes's argument goes wrong that we will have good grounds for setting our faces against that dualistic inclusion and proceeding and perhaps more materialistic path.
