Our mind-body problem is not just a difficulty about how the mind and
body are related and how they affect one another. It is also a
difficulty about how they
can be related and how they
can
affect one another. Their characteristic properties are very different,
like oil and water, which simply won’t mix, given what they are.
Mind: What is characteristic of a mind, Descartes claims, is that it is conscious, not that it has shape or consists of physical matter. Our bodies are certainly in space, and our minds are not, in the very
straightforward sense that the assignation of linear dimensions and
locations to them or to their contents and activities is unintelligible.
Body: According to Descartes, matter is essentially spatial, and it has the
characteristic properties of linear dimensionality. Things in space have
a position, at least, and a height, a depth, and a length, or one or
more of these. Mental entities, on the other hand, do not have these
characteristics.
Objection to mind-body problem: The difficulty, however, is not merely that mind and body are different.
It is that they are different in such a way that their interaction is
impossible because it involves a contradiction. It is the nature of
bodies to be in space, and the nature of minds not to be in space,
Descartes claims. For the two to interact, what is not in space must act
on what is in space. Action on a body takes place at a position in
space, however, where the body is. Apparently Descartes did not see this
problem.
- Our minds are not physically connected to our bodies! How could they be,
if they are nonphysical? That is the point whose importance Princess
Elisabeth and Gassendi saw more clearly than anyone had before them,
including Descartes himself.
Significance of the problem: That this straightforward test of physicality has survived all the
philosophical changes of opinion since Descartes, almost unscathed, is
remarkable.
Reference: Descartes and the discovery of "The Mind-Body Problem"