Cartesian Dualism - Handout

PHI 412/512, Bruton

Cartesian Dualism - Handout

Descartes holds that there are fundamentally two kinds of things in the world - minds and bodies. He is, in other words, a substance dualist. To say that there are fundamentally two kinds of thingsis to say that things of one kind cannot be reduced to the other. (Wind is not metaphysically fundamental in this way, for example. Wind is really just moving air - true propositions about the wind can be reduced to (or reworded in terms of) propositions about moving air. Similarly for rainbows, automobiles, and a host of other things that, we think, are made up of other things that are ontologically more basic.) Another relevant kind of dualism is property dualism. (A property is that which can be predicated of something. For example, when I say, “Grass is green,” I predicate or attribute green-ness - a property - to grass.)The property dualist thinks that there are fundamentally two different kinds of properties that things have - again, fundamentally, because the thought is that properties of one kind cannot be reduced to the other. Descartes is also a property dualist, because he thinks that neither mental properties nor physical (or corporeal) properties can be reduced to the other. The property of feeling pain, or believing that snow is white, for example, are not just properties of one’s brain for Descartes - they are properties of minds. On his view, properties of each kind are always and only possessed by substances of the corresponding kind. Descartes thinks mental properties, for example, can be possessed only by minds.Substance dualism seems to imply property dualism. (Without fundamentally different kinds of properties, what sense could be made of the idea that we have fundamentally different kinds of substances?) But one could be a property dualist without being a substance dualist. One might think, for example, that humans are thinking animals, possessing (somehow) both mental and physical properties, while denying that properties of one kind can be reduced to the other. (Spinoza will give us an interesting version of substance monism combined with something like property dualism.)

To get a feel for what Descartes’ substance dualism really amounts to, it is helpful to contrast it with some other views. Many people (philosophers and otherwise) today are materialists, like Hobbes. Materialists think that everything is ultimately physical. The materialist might permit talk of minds (as a kind of shorthand way of talking), but believes that minds and mental states ultimately consist only of brains and brain states. Thus, if we ask, “Are minds nothing but brains?” Descartes will say “no,” but the materialist will say “yes.” An idealist, on the other hand, believes that everything is ultimately mental. All seemingly physical properties and substances are really just mental properties and minds. Not too many people today are idealists in this sense, but idealism is a very prominent view in modern philosophy. Berkeley, Leibniz, and Kant, each in different ways, are all idealists. Arguably, so too is Hume.

Descartes associates personhood with particular minds - for him, I really am just my mind. In the end, Descartes is also going to admit that he (and the rest of us) also has (have) a body, but that his body is not essential to him being him, and yours is not essential to you being you. This is a problematic view. On the assumption that minds interact with bodies, as they certainly seem to, how can this be? How can a non-extended, non-physical thing - a mind, which strictly speaking does not exist at any place, since only physical extended things exists at places - interact with an extended, physical thing?(This is the 800 lb. elephant sitting right in the middle of Descartes’ dualism, the so-called interaction problem.) In fairness, though, many of our common sense views suggest dualism, and Descartes’ dualism arguably makes better sense of two theologically-oriented ideas than materialism. How can I survive my death (e.g., in heaven)? This is easy for Descartes - my mind lives on even though my body perishes - but difficult for a materialist, unless the materialist wants to posit bodily resurrection for all of those going on to the next life. Second, if one thinks that God is immaterial and yet God created the material world, the interaction problem will arise (on a divine level) even if one is a materialist about everything else in this world.Furthermore, if one thinks that events in the physical world are causally determined, it’s hard for a materialist to make sense of free will in any robust (non-compatibilist) sense. And property dualism has some intuitive support, too. One a simple version of materialism, mental states just are brain states. So the mental property of being in pain or believing that p ends up identified with these and those brain states. A property dualist like Descartes can plausibly argue, however, that mental states can’t just be brain states, because mental states have a meaning, a content, or a “feel” – something that would get left out in the attempted reduction to brain states. Brain states can’t be about anything, but mental states often are.

Because dualism is not without its advantages and yet tough to swallow, philosophers have carefully scrutinized Descartes’ arguments for dualism. The first, which Descartes suggests is not his “official” argument, occurs in Med. II. There it looks like Descartes argues from the premises that he cannot doubt that he has a mind and yet can doubt that he has a body, to the conclusion that he really is just a mind. The general suspicion about this move is that it’s not legitimate to go from a claim about what I or anyone else can or cannot doubt to a claim about the nature of reality. Doubts, after all, are psychologically variable. Today I might doubt something I didn’t doubt yesterday, or that you have never doubted. Personal psychology, in other words, is a shaky foundation on which to build metaphysics.

To diagnose the problem with this Med. II argument more rigorously, let’s think about it this way:

1. I cannot doubt that I have (or I am) a mind.

2. I can doubt that I have (or I am) a body.

3. Therefore, I am nothing but a mind.

On the face of it, this line of argument seems pretty much hopeless. But we can make it look a little better if we add a premise that Descartes does not mention (but would certainly accept) - the Principle of the Identity of Indiscernibles. (Principle IdIn) This principle (as commonly understood) claims two things: a) different things must have different properties, b) identical things have identical properties. (A word of caution: we use the word ‘identity’ ambiguously. Sometimes, by ‘identical’ we just mean qualitatively similar. We might say, for example, that this Diet Coke can is identical to that one - both are the same shape, have the same colors painted on, etc. But at the same time we realize that, strictly speaking, they are not identical - they are two, not one. This, though, is not really a counter-example to IdIn.IdIn holds only for “numerical identity,” or identity “strictly speaking,” not qualitative identity.)Our two “identical” cans, sure enough, have some differing properties – at least spatio-temporal properties. (This one, for example, is a little closer to the door than that one, and they were manufactured at different times, and are comprised of different atoms, etc. Or this one’s mine, and that’s yours.) The other thing we need to do to help Descartes out here is to think of “can be doubted” and “cannot be doubted” as properties of things. We then get this:

1. Things with different properties are different things. (IdIn)

2. My mind has the property of indubitability.

3. My body, though, lacks the property of indubitability.

4. Thus, my mind and my body are different things. (from 1, 2, 3)

And, since Descartes claims to know that he exists and has (or is) a mind, he concludes that he’s just a mind. Or at least that’s all he can claim to know about himself at this point.

Even dressed up though, Descartes’ reasoning still seems flawed. A common diagnosis of the mistake stems from an insight into what are called propositional attitudes. A propositional attitude, basically, involves a cognitive relation to a proposition as its object. (More on them can be found at Stanford: Their form is always:

X has some mental state that p, where p is a proposition and ‘has some mental state’ includes mental states such as beliefs, desires, knowledge, and so forth.Propositional attitudes are usually expressed using a ‘that’. So, here are some examples:

Sam believes that he exists.

Josh wants that USM wins the game. (We wouldn’t normally put it in this way, but this is logically equivalent to ‘Josh wants USM to win the game.’)

Malachi hopes that his workday is almost over.

The insight is that ordinary logical relationships that propositions possess are distorted when we nest them in propositional attitudes. Here’s a valid (and sound) argument:

Lincoln was assassinated.

Lincolnwas identical with the 16th president.

Therefore, the 16th president was assassinated.

So far so good - the conclusion follows with certainty given the truth of the premises. But now look:

Donbelieves that Lincoln was assassinated.

Lincoln was identical with the 16th president.

Therefore, Don believes the 16th president was assassinated.

The conclusion might be false and yet the premises both true. The point of this, in relation to Descartes’ argument, is to say that inferences involving identity claims and IdIn don’t always work after we’ve started nesting propositions into propositional attitudes. Since “I doubt that p” and “I do not doubt that p” are propositional attitudes, Descartes’ Med. II argument is questionable.

In Med. VI we get two new arguments for substance dualism. The most important one, which Descartes hints is his official “proof” of the distinctness of mind and body, happens at p. 50, col. 2 (middle). There has been considerable scholarly discussion of what the argument actually is and where it goes wrong. Here’s a somewhat simple-minded rendering of the argument:

1. If I can C + D perceive one thing existing without another, then they can exist separately (at least God could make it so).

2. Things that can exist separately are really distinct.

3. I can clearly and distinctly perceive my mind existing without my body.

4. Thus, my mind and my body can exist separately. (1, 3)

5. Thus, I am really distinct from my body. (2, 4) (I am essentially a mind, but only accidentally a body).

One way of diagnosing the problem with this argument is to think that it involves a sort of slide from a logical point to a metaphysical point. The first premise seems to say that the fact that two things can be conceived of as logically distinct means that it is logically possible that they can exist apart. Here I think we should agree with Descartes: it seems logically possible that my mind can exist without my body. (Saying that something is logically or conceptually possible is not saying much; it just says there is no logical contradiction involved in the separate existence of mind and body. This is what the medievals referred to as a “distinction in reason.”) The slide seems to happen in the second premise. The fact that it is logically possible for my mind to exist without my body doesn’t mean that they are distinct in the metaphysical sense, that they are different substances. (Or what the medievals called a “real distinction.”) By analogy, it seems logically possible that I am not the eldest son of Roger and Carol, but it wouldn’t follow from this that I am a different person from the eldest son of Roger and Carol. I am, in fact, their eldest son.

Descartes’ reply, as implied in his response to Arnauld’s criticism of this argument, is likely to be that while in general metaphysical distinctness does not follow from separability in the logical sense, that when claims of essences are involved, it is a different story. In terms of the counter-example, Descartes is likely to question the claim that it is logically possible that I am not the eldest son of Roger and Carol. To claim that x is something’s essence (on Descartes’ view) is to claim, basically, that without x the thing would not be the thing that it is. So if being their eldest son is part of the essence of who I am, it is not logically possible that I am not their eldest son, and the counter-example fails. As you can see, this response gets us into a debate about what it is for something to be essentially x.

So let me conclude with a rendering of the argument by Margaret Wilson, who is trying to reformulate it in such a way as to avoid the slide from logical possibility to metaphysical distinctness. Wilson argues that the argument is more cogent than its critics have typically realized:

(1) If A can exist apart from B, and vice versa, A is really distinct from B, and B from A.

(2) Whatever I can clearly and distinctly understand can be brought about by God as I understand it.

(3) If I can clearly and distinctly understand the possibility that A exists apart from B, and B apart from A, then God can bring it about that A and B exist in separation.

(4) If God can bring it about that A and B exist in separation, then A and B can exist apart, and hence by (1), are distinct.

(5) I can clearly and distinctly understand the possibility of A and B existing apart from each other, if: there are attributes  and , such that I clearly and distinctly understand that  belongs to the nature of A, and  belongs to the nature of B, and that , and I clearly and distinctly understand that something can be a complete thing if it has  even if it lacks  (or has  and lacks ).

(6) Where A is myself, and B is body, thought and extension satisfy the above conditions on  and  respectively.

(7) Hence, I am really distinct from body (and can exist apart from it).

(Margaret Wilson, “Descartes: The Epistemological Argument for Mind-Body Distinctness,” in Ideas and Mechanism: Essays on Early Modern Philosophy. Princeton, 1999: 84 – 93.)