Flanagan on Descartes’ Modal Argument for Dualism

I’ve just started reading through Owen Flanagan’s book The Science of the Mind and he presents Descartes’ Modal Argument as follows:

1. I cannot possibly doubt that I exist as a thinking thing. (This was established as we tried to doubt our existence and found ourselves, therefore, affirming it.)
2. I can doubt, however, that I have a body, and thus that I exist as a physical thing.
3. Therefore, thinking is essential to what I am. My body is not. Furthermore, I know my mind more easily than I know my body. “From this I knew that I was a substance the whole essence or nature of which is to think, and that for its existence there is no need of any place, nor does it depend on any material thing so that this ‘me,’ that is to say, the soul by which I am what I am, is entirely distinct from body, and is even more easy to know than the latter; and even if body were not, the soul would not cease to be what it is.”

Flanagan goes on to praise the intuitive merit of the argument based on the epistemological principles laid down in earlier passages of the book. He does believe it has a problem, however, and claims that it has a missing premise. I claimed as much in an earlier post, but his missing premise ends up looking much different than mine based on the alternative construction of the argument. He calls this missing premise “alpha”:

Alpha: when an entity is known for certain to have property x, but not known for certain to have property y, then x is essential to the entity and y is not.

Obviously, this assumption is false. He gives the example of a geometry student who comes to believe- with certainty- that a set of three Cartesian coordinates makes a triangle, but fails to see that the internal angles of this triangle add up to two right angles. The problem is an epistemic problem.

I see this objection as a cousin to the host of objections relating to conceivability-entails-possibility. Likewise, the best answer to this objection is fairly weak: either you simply see that it is possible to exist without your body or you don’t. I do see that it is possible (I am not simply failing to see that it is impossible). I am then warranted in my belief that I am not essentially a body.

Edited to Add: While I think Alpha is wrong as a fast and tight principle, it seems that if something fits the criteria laid out in the principle, one has reasons (and probably good reasons) for suspecting that it describes essential properties. If all we had was Descartes’ argument -AND- you were convinced that the second premise (I can doubt, however, that I have a body, and thus that I exist as a physical thing) is true then we would be epistemically in the clear for believing that we are not essentially body.

Descartes presents the replacement argument to the princess

I’ve been discussing Descartes’ version of the replacement argument with a chap here, and since I can’t find an online copy of the dialogue I’m going to type out the relevant passage from a printout. This is from a book no one will probably ever see again, but I printed off the passage from a friend who stumbled upon it.

Elizabeth: How are they connected?
Descartes: Well, it’s really to do with possibilities. If it is possible for thinking to go on apart form a body then…
E: [Interrupting] But is it possible? That’s the question.
D: All right, I’m coming to that. I did say “if”. If it is possible for thinking, and the body, to exist in separation then…
E: [Impatiently] Yes, yes, then what-does-the-thinking isn’t the body. I can quite see that. But what you’ve got to do is to get rid of the “if”. That is, you’ve got to show it to be possible for thinking to go on apart from a body.
D: Precisely, and that is where what I know and don’t know, comes in.
E: Go on.
D: Well, I know certainly that I am thinking and at the same time I can doubt that I have bodily attributes. So I can perceive the one thing, the thinking, apart from the other. And since this perception is clear and distinct it must be possible for the one thing to exist apart from the other.
E: Just a moment. You said :since this perception is clear and distinct.”
D: Yes.
E: And therefore you really are no more than a thinking thing?
D: Exactly.
E: All right. Well now, isn’t is possible that your perception is clear, but only as far as it goes? And that it doesn’t go far enough for you to know the truth? In other words, isn’t it possible that you really do have bodily properties although your knowledge of yourself doesn’t go beyond your mental properties.
D: No. You must distinguish between clearness and completeness. Certainly there may be things about me which I haven’t clearly perceived. But that doesn’t affect what I have clearly perceived. And, having clearly perceived that I am a thinking thing, I know that I can exist as such. That is, I know that what I am certain of- my intellectual faculty- is enough for me to exist with. And if it is enough for me to exist with, then I really am distinct from anything bodily.
E: So, the principle of your argument is: if I can clearly perceive something to be such-and-such while I cannot clearly perceive it to be so-and-so, then it can exist simply as such-and-such.
D: Yes.

This is a fascinating exchange that, as far as I can tell, has many components of the discussion that has cropped up around Plantinga’s version. More on that as we progress into an analysis of Plantinga’s presentation of the argument.

Descartes on the Replacement Argument?

(You can read the context here, but I’m taking the translation from the IEP)

[T]here is a great difference between the mind and the body, inasmuch as the body is by its very nature always divisible, while the mind is utterly indivisible. For when I consider the mind, or myself in so far as I am merely a thinking thing, I am unable to distinguish any parts within myself; I understand myself to be something quite single and complete….By contrast, there is no corporeal or extended thing that I can think of which in my thought I cannot easily divide into parts; and this very fact makes me understand that it is divisible. This one argument would be enough to show me that the mind is completely different from the body…. (AT VII 86-87: CSM II 59).

The IEP sets up his argument in the following way:

1.I understand the mind to be indivisible by its very nature.
2.I understand body to be divisible by its very nature.
3.Therefore, the mind is completely different from the body.

It doesn’t take much to realize this argument is missing something and is overstating its case. The conclusion does not follow without the following hidden premise:

(HP) If the mind and body have different properties, then they are completely different.

However, I don’t see that premise as true at all. In fact, it is extremely counter-intuitive. But we can mend the argument in a way Descartes would probably object to:

1. The mind has the property of being essentially indivisible.
2. The body is has the property of being essential divisible.
3. If the mind and body are identical, they have the same essential properties.[The law of indescernibility of identicals: x = y → (∀F)(Fx ↔ Fy)]
4. The mind and body do not have the same essential properties [from 1,2]
.: The mind and body are not identical [MT from 3,4]

Plantinga’s Replacement Argument

*Just a friendly warning*

I’m going to take a few days (or so) looking at Plantinga’s replacement argument along with related issues (Kripke, van Inwangen). I’ll have something by tomorrow afternoon.

Carry on.