Rene DescartesThere can be no doubt that modern Western thought owes an incredible debt to the work of the French philosopher, Rene Descartes.  His Meditations on First Philosophy revolutionized the method and scope of rational inquiry and has had lasting repercussions into the present day.  Within the Meditations Descartes employs a strict axiomatic method in search of a secure foundation for knowledge; a foundation which he eventually discovers in his famous statement, cogito ergo sum: “I think therefore I am”.  An interesting byproduct of this discovery is Descartes’ consequent assertion that it is easier to know that one has a mind then that one has a body.  Indeed, the title of the second Meditation is, “Of the Nature of the Mind; And That It Is More Easily Known than the Body”.  But is this statement implied by Descartes’ cogito?  I believe that it is not and that Descartes’ reasoning is fallacious in regards to his epistemological distinction between the mind and the body.           

Before investigating the above claim, it is important to review the process of reasoning that led to its assertion.  Descartes begins the Meditations with radical doubt.  Indeed his stated purpose is to “apply [him]self earnestly and freely to the general overthrow of all [his] former opinions.” His criterion for knowledge is strict foundationalism: he will only accept propositions that cannot be doubted or propositions that are built upon other indubitable propositions.  He is quite literally seeking to demolish the structure of his beliefs so that he can reconstruct them upon a certain foundation.  The epistemological wrecking balls that he employs are various arguments that can be traced back to the ancient skeptics.  At the end of the day – after meditating upon insanity, dreams, and evil demons – Descartes has effectively stripped himself of certainty concerning his former beliefs.

A new day provides the second Meditation and the famous discovery of the cogito.

So that it must, in fine, be maintained, all things being maturely and carefully considered, that this proposition I am, I exist, is necessarily true each time it is expressed by me, or conceived in my mind.

There has been much debate over what Descartes was exactly trying to communicate by this statement.  Some have insisted that Descartes is presenting an argument here, while others believe that he is simply stating a self-evident truth which he has discovered.  While this debate is both interesting and important, it really makes no difference in regards to this post.  Suffice it to say that Descartes (whether in formal argument or not) is asserting that it is a necessary truth that whenever he thinks, he exists.  This is an impressive feat of reasoning to be sure, but his assumption that the mind is more easily known than the body does not follow from it.

            Descartes’ claim can be expressed in the following argument:

  • 1. I cannot doubt the existence of my mind.
  • 2. I can doubt the existence of my body.
  • 3. Therefore, the mind is more easily known than the body.

The first premise follows from the cogito.  Descartes states that he cannot doubt his own existence because, necessarily, whenever he doubts he is thinking, and whenever he is thinking he exists.  Therefore he exists as a mind, or a “thinking thing”.  In the first Meditation, however, he has already established that he cannot be certain of the existence of his body.  Therefore the knowledge of his mind is more certain than the knowledge of his body. 

            It is important to point out a major assumption that Descartes is making here: he assumes that the mind and body are distinct substances.  It appears that he bases this distinction upon a principle that was later articulated by the German philosopher Gottfried Leibniz.  This principle, known as Leibniz’s Law of the Indiscernibility of Identicals can be stated thus:

Necessarily, for any X and Y, if X is identical with Y, then for any property, P, X has P iff Y has P.

It follows then from the above principle that, if the mind and body possess different properties, they must be distinct substances.  Descartes appears to hold to something like the following argument:

  • 1. My body possesses the property of being doubted by me.
  • 2. My mind does not possess the property of being doubted by me.
  • 3. Therefore, according to the Indiscernibility of Identicals, my body is distinct from my mind.

It is only after he assumes the distinction above that Descartes can then go on to argue that the mind is more easily known than the body.  However, this argument is based upon the fallacious idea that dubitability implies distinction. 

            Consider the following argument:

  • 1. Samuel Clemens possesses the property of being doubted by me that he is the author of A Connecticut Yankee in King Arthur’s Court.
  • 2. Mark Twain does not possess the property of being doubted by me that he is the author of A Connecticut Yankee in King Arthur’s Court.
  • 3. Therefore, according to the Indiscernibility of Identicals, Samuel Clemens is not the same person as Mark Twain.

Of course this argument is clearly absurd since we know that the names “Samuel Clemens” and “Mark Twain” do indeed refer to the same person.  It is this same reasoning, however, that Descartes employs in distinguishing the body from the mind.  Just because he doubts the existence of his body and is certain of the existence of his mind, it does not follow that they are two different substances.

            It appears, therefore, that Descartes was wrong in asserting that the mind is more easily known than the body based upon the cogito.  What he was perceiving as his “body” and as his “mind” may well have been the same substance with two different names.  This is not to imply that the body and mind are the same, however, just that one cannot make this distinction based upon Descartes’ assumption.  And if the mind and body are indeed the same substance, then it makes no sense to say that one is more easily perceived than the other.