This paper will discuss the dualism’s Divisibility Argument. This argument
relies on Leibniz’s Law and uses a different property to prove the
distinctness of brain states of mental states. Mary, who is a materialist,
presents several objections to that argument. Her main objection corresponds to
the first/third-person approach. She believes that Dave presents that argument
only from the first-person approach, which is introspection, and totally
disregards the third-person approach, which is observation of another mind.
Mary’s objections will follow by the Dave’s response on them from the
dualist’s point of view. The purpose of the Divisibility Argument is to prove
that mental states are different from the brain states. My body, which includes
my brain, is divisible. However, I cannot conceive of my mind as divisible.
Therefore, my mind is distinct from any part of my body. Descartes was the first
who established the Divisibility Argument. He held that the two components which
constitute man had an independent origin and are of a fundamentally different
nature. The body is divisible, since it can be separated for example, my leg or
my hand can be cut off; my brain can be cut on half. However, the idea of the
divisible mind is inconceivable. This argument relies on the Leibniz’s Law. It
is a principle about identity, which says, “if an object or event X is
identical with an object or event Y, then X and Y have all of the same
properties.” So if X and Y have any different properties, then X can not be
identical with Y. Divisibility Argument uses a different property to prove the
distinctness of brain states and mental states: the property of being
indivisible. In this case, the mind has a property and brain lacks it. The body
can be divided, however, it cannot be done with the mind. Mary has several
objections to this argument. First, she believes that the mind is an entity,
which is composed of several mental states: thoughts, beliefs, memories,
desires, etc. Mary strongly disagrees with Descartes’ claim that the mind
employs itself in its different properties: willing, desiring, understanding,
and so on. Secondly, she clarifies the meaning of the word “conceive” in the
Dave’s argument. The term “conceive” might mean either “imagine” or
“understand.” Imagining literally involves “forming an image of” or
“picturing” in one’s mind, whereas understanding is more “conceptual”
and does not require the ability to picture something. In case, Dave interprets
the word “conceive” as “imagine” in the second premise of the argument,
this premise becomes untrue. The fact that he cannot imagine something to be the
case does not make it true in everyone’s case. Different minds can imagine
different things. However, if Dave implies “understand” as a meaning of
“conceive” the second premise still remains doubtful. The fact that Dave
cannot understand it does not exclude the possibility that someone else is
capable to think of his mind as having parts. The next major objection to the
Divisibility Argument concerns first/third-person approach. Mary rejects
Dave’s assumption that the true nature of the mind can be understood solely
through introspection or from the first-person approach. She claims that things
that cannot be conceived through the first-person approach, which is
introspection, can be understood or investigated through the third-person
approach, which is observation and science. Therefore, even if it is true that
the mind cannot be conceived as divided from the first-person perspective, it is
possible that it would be the opposite from the third-person perspective. The
perfect example of that case is the multiple personality disorder. This is the
clear case where the third-person perspective reveals the true nature of a mind
as divided regardless of how it seems from the first-person perspective. As a
response to Mary’s objection, Dave agrees that the second premise in the
argument does not have always a true value that makes the argument unsound.
Therefore, he changes it to “I cannot conceive of my individual mental states
as having parts.” In the case of the first/third-person approach, Dave relates
to the multiple personality disorder as a case with several minds rather than
one divided mind. In my opinion, Dave does not satisfactorily respond to the
Mary’s objections since he does not give a good reasoning for his point of
view. However, I do believe that the mind is indivisible since there is no such
thing as part of mind. Mind and matter have fundamentally different natures:
matter, which is extended, divisible, passive, and law-like; and mind, which is
unextended, indivisible, active, and free. I definitely agree with Descartes
that the soul occupies the whole body in all its parts, so the reduction of the
body in any way does not reduce the soul. Thoughts, feelings, desires and so on,
are all properties of the mind but not its parts.