The upshot of an earlier argument was that I cannot be a soul-body composite. So if I have a soul, then I am identical with it. This is a conclusion that Roderick Chisholm also arrived at:
If we say that (1) I am a thinking being and (2) that thinking beings and souls are the same, then we should also say (3) that I am a soul; and therefore (if we take 'have' in its ordinary sense) we should say (4) that I do not have a soul. ("On the Simplicity of the Soul," Philosophical Perspectives 5, 1991, p. 178)
If this is right, then hylomorphic dualism is untenable as well as any substance-dualist position according to which I am a composite of two substances. If I have a soul, speaking loosely, then I don't have it, speaking strictly, but am identical to it. But why suppose that one either has or is a soul? Why can't one be a brain-body composite? For essentially the same reasons that I gave last time for my not being a soul-body composite.
First an argument to the conclusion that I am not identical to a brain-body composite, then an argument that I am not identical to my brain.
Suppose for reductio 1) that I am a brain-body composite and 2) that the brain is that in me which thinks. (Surely, if a physical part of me thinks, it is not the liver or heart but the brain.) Then 3) I think in virtue of my brain thinking. But 4) my brain is a proper part of me, whence it follows 5) that I think in virtue of the thinking of a proper part of me. Now 6) that which is a proper part of me is numerically distinct from me. Therefore, 7) I think in virtue of the thinking of something numerically distinct from me. But 8) this is absurd. Why? For the reasons given, mutatis mutandis, in the earlier post. Therefore, 9) if the brain is that in me which thinks, then I am identical to my brain.
But could I be identical to my brain? If I am not identical to my brain plus the rest of my body, then I am not identical to my whole brain either, since not every part of my brain is involved in thinking. But the real problem is that it makes little or no sense to suppose that the brain or any part of it is thinking when I am thinking. My brain is no more thinking when I am thinking than my eyes are seeing when I am seeing. (And my eyes are no more seeing when I am seeing than my glasses are.) I see with or by means of my eyes just as I hear with or by means of my ears; but when I see something it is not my eyes that see it. I see it. As Chisholm puts it, "Those physical organs do not do my seeing and hearing for me." (171) The same goes for the brain. If I hope you find this post interesting, then it is I who hope this, not my brain.
I am not denying that the brain is causally necessary for thinking to occur. The point is rather that the brain cannot be the subject of thinking, that in me which thinks. I, the subject of thinking, cannot be identical to my brain. This can be argued Kripke-style:
a. If x = y, then necessarily x = y. (Principle of the Necessity of Identity)
b. If I = my brain, then necessarily I = my brain. (From (a))
c. I can conceive myself existing without my brain existing.
d. What is conceivable is possible.
e. Possibly, I exist but my brain does not. (From (c) and (d))
f. Possibly, I am not identical to my brain. (From (e))
g. I am not identical to my brain. (From (b) and (f) by Modus Tollens)
Bill,
A minor comment: in (a) you need to add the provision that 'x' and 'y' are rigid and then in (b) you need to show that the pronoun 'I' is rigid and that whatever term used to refer to the brain in the right hand side of the identity is also rigid. For instance, if we substitute non-rigid description for 'x' and 'y' in (a), then it will be false.
(Note: I say non-rigid descriptions because some in the literature maintain that there are rigid descriptions. I am not confident that there are, but just in case, I added this proviso).
peter
Posted by: Account Deleted | Saturday, May 09, 2009 at 06:45 AM
Peter,
But are 'x' and 'y' ever used as variables whose substituends are descriptions? The substituends of individual variables such as 'x' and 'y' are standardly taken to be names, where names are rigid designators. Isn't that right? But you are right that if descriptions *were* substituted for 'x' and 'y,' then (1) could come out false, e.g., this is false: 'If the fastest runner in Jerome = the skinniest woman in Jerome, then necessarily the fastest runner in Jerome = the skinniest woman in Jerome.'
How could 'I' be nonrigid? When a person tokens 'I,' he refers to the same individual in every possible world in which that individual exists. 'The best chessplayer in Gold Canyon' refers to me but nonrigidly. I fail to see how 'I' used by me could fail to refer to me in every world in which I exist.
Same with 'my brain' which can be analyzed in terms of the first person singular pronoun.
Are there rigid descriptions? I should think so. How about 'that than which no greater can be conceived'?
Posted by: Bill Vallicella | Saturday, May 09, 2009 at 01:16 PM
Addendum: I'm not saying that it is standard doctrine that names are rigid designators, but that it is standard doctrine that the substituends of individual variables such as 'x' and 'y' are names. Or are there philosophers whose notation allows a description to be a substituend for 'x'?
Posted by: Bill Vallicella | Saturday, May 09, 2009 at 01:19 PM
Bill,
I certainly think you are right about 'I' being rigid. Regarding 'my brain', that is somewhat less obvious, but I think we can grant that without much risk.
Typically, the substituents of individual variables are terms which designate an individual object including names or descriptions; hence, in general, the provision that the substituents should be rigid is always added.
peter
Posted by: Account Deleted | Saturday, May 09, 2009 at 01:56 PM
Peter,
You may be right as to your main point, but I wonder if you have a passage in Kripke or somebody else to which you can refer me.
Posted by: Bill Vallicella | Sunday, May 10, 2009 at 01:56 PM
Bill,
The principal reference is "Naming and Necessity", but I do not remember page number. In Standford Encyclopedia of Philosophy there is an article about rigid designators (just type in 'rigid designators') and the article will be the first one that comes up. In the first section the author states the point I have made.
Intuitively the reason rigid designators turn an identity statement necessary true, if it is true, is because a rigid designator refers to the very same object to which it actually refers in all possible world in which the object exists; so if an identity statement flanked by two rigid terms is true in the actual world, then the terms will refer to the same object in all other possible worlds in which it exists and thus the identity statement is going to be true in all of these worlds. The reason the same does not hold for non-rigid descriptions is because the reference of such a description is liable to vary from world to world and therefore the object picked out by a description is not the same throughout the worlds.
peter
Posted by: Account Deleted | Sunday, May 10, 2009 at 06:45 PM
Peter,
I read the first section of the SEP article, but I don't see that it addresses the question we are discussing at all. Here again is
(a): a. If x = y, then necessarily x = y. (Principle of the Necessity of Identity).
You say I have to add that 'x' and 'y' are rigid. I claim that that
addition is not necessary, because 'x,' 'y','z' are individual variables (not individual constants, and not property variables)whose SUBSTITUENDS (not to be confused with VALUES) are understood to be logically proper names, not descriptions.
Posted by: Bill Vallicella | Sunday, May 10, 2009 at 07:51 PM
Bill,
If we grant that names are rigid and that the substituends of the variables are to be only names, then you of course get the result that any instance of (a) will have only rigid designators flanking the identity sign. o then we agree on the central issues.
peter
Posted by: Account Deleted | Sunday, May 10, 2009 at 08:25 PM