Substance dualism is a belief that mind and body are
completely separate and different in nature, i.e. they are different
substances. This view was proposed by Rene Descartes and is the
impetus for the mind/body problem. It is a troublesome position
because two separate substances cannot interact causally, where the
mind and body clearly do interact causally. This leads to the concept
of substance monism.
Descartes's Argument for Substance Dualism
Descartes begins his argument for substance dualism by establishing
his existence as a certain fact, impossible to doubt. He does this
through the process of discarding all that can be
doubted and finding that he cannot doubt that he
exists. Having established this, he goes on to investigate what this
"I" who he has proven to exist is, and through the same systematic
removal of all that can be doubted establishes that the essential
characteristic of this "I" is that it is a thing that thinks.
So, since his essential nature is as a thinking thing, he
questions whether embodiment is a necessary part of his
existence. He requires that his essential nature be completely
certain, and thus, since he can doubt the existence of his body and
concieve of himself as a disembodied soul, his body is not
part of his essential nature and therefore must be separate from his
mind, whose existence is certain and impossible to doubt. Hence, mind
and body are separate substances.
Rebuttal to Descartes's Argument
Descartes considers the fact that he can doubt the existence of his
body as sufficient proof that it is unnecessary and thus
separate. If we accept Descartes's argument as to why the body is
unnecessary, it does not necessarily follow that therefore they must
be separate. Having a left big toe is unnecessary in the sense that
I can conceive of my left foot only having four toes, but this does
not mean that it is a separate substance from the rest of my
foot. Instead, it only requires the weaker claim that it is
separable from the rest of the foot, i.e. that it can be made to be separate from the rest of the foot.
A Word on Substance Dualism and Identity Theory
Without this concept of substance dualism, it remains unnecessary
to requirer that mental events be identical to
physical events. Lacking substance dualism, the concept of the mental
and the physical existing in inherently separate realms must be
discarded, but it is not required to reduce mental
events to physical events. The two forms of event have different
characteristics. Mental and physical events retain a conceptual difference even if they are not held to completely
separate domains of existence.
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This writeup is copyright 2004 D.G. Roberge and is released under the Creative Commons Attribution-NoDerivs-NonCommercial licence. Details can be found at http://creativecommons.org/licenses/by-nd-nc/2.0/ .