Descartes and Philosophy of Mind: The Conceivability Argument and the Divisibility Argument

Introduction and Context:
Watch the Video first:

So, is the brain the mind?  Is the mind the brain?  Are they separate things?  If so, are you your brain or your mind?  Or are you somehow both but they aren’t the same thing?  Are you confused?

Poor Karl.  Lets try to help him clear up his confusion.  Fortunately, we have philosophy at our disposal to provide some answers in our time of need (where else could you possibly go?).  To get at some kind of an answer lets start with Descartes who thought he had a solution to this problem.  The short answer, as you should know by now, is that you are a mind, not a body.  

Descartes proposed 3 main arguments for what is called substance dualism which is the position that the mind and the body (i.e., brain) are two completely different types of things (i.e, substances).   Because my main goal is simply to present the general position, for our purposes we’ll only look at two of the arguments.

The Conceivability Argument (6th Meditation)
The conceivability argument rests upon two similar principles: (a) The doctrine of clear and distinct is that anything that can be clearly and distinctly conceived of is possible and therefore can, in the “real world” correspond perfectly with one’s understanding of it.  Lets not worry too much about this part…The other principle plays a more important role:  Hume’s law is that if we can conceive of something then it is logically possible.

Ok, with those principles in “mind” lets take a look at a stripped down version of the argument: 

(P1)  I conceive that I, a thinking thing, can exist without my extended (i.e., physical) body existing.

(P2)  Anything that I can conceive of is logically possible.
(P3)  If it is logically possible that X (mind) exists without Y (body), then X (mind) is not identical to Y (body).
(C)   Therefore, I, a thinking thing, am not identical with my extended body.

Recall from the 1st meditation where Descartes shows that we can doubt everything, including the existence of our own physical body, except that we think and that we exist. Because we can conceive of ourselves as existing without having a body, we must not be identical to our body.  Since we are not identical to our body, our minds and our bodies must be 2 completely different sorts of things (he calls them “substances”).

Most philosophers reject this argument because it relies on Hume’s law (P2) which most contemporary philosophers also reject.  Conceivability is not sufficient for logical possibility. 

Another reason for rejecting the argument is that while Descartes may be correct in that thought is essential to mind and extension is essential to bodies, it doesn’t follow that this is all there is to each.  He argues that since the essence of mind is thought, he “can infer correctly that my essence consists solely in the fact that I am a thinking thing.”  But just because thought is an essential property of mind it doesn’t necessarily follow that this is the only property of mind.  In other words, he can’t make that inference. 

Alright, for our purposes, this should suffice…

Next argument:
The Divisibility Argument
We can present it simply like this:

(P1)  All extended things are divisible. (It’s possible to divide the body or matter into parts) 

(P2)  Minds are not divisible.  (When you introspect, you can’t distinguish parts of the mind within yourself).
(P3)   Although it appears as though my mind and body are united, if I were to remove body parts, “nothing would have been taken away from the mind”, thus, minds are not extended. 
(C)  Therefore, it follows that the minds are distinct substances from bodies.

Most contemporary philosophers (and brain scientists) reject (P3).  We know that if we remove parts of the brain, part of our “mind” will also be removed.  Also, when the corpus callosum (the bundle of nerves connecting the two hemispheres) is removed, the “mind” seems to divide into two separate consciousnesses. 

While it’s interesting to dissect what when wrong in Descartes arguments, the more interesting philosophical area is to look at the problems that arise if we accept (or reject) dualism.  Recent psychological studies show that most people are natural dualists (i.e., they believe in a non-material mind/soul/spirit/etc…).  Not that it matters what the unwashed masses think (I kid! I kid!) but it’s interesting to inquire what sorts of problems come about from accepting dualism.  Very early on, the very astute Princess Elizabeth of Bohemia noticed some of these problems and presented them to Descartes in written correspondence…which is the topic of the next post…

3 thoughts on “Descartes and Philosophy of Mind: The Conceivability Argument and the Divisibility Argument

  1. From the analysis herein, can one infer that Hume's law of the logical possibility of anything base on its conceivability is a justification of Descartes clear and distinct idea as a mark for possible existence of what there is?


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