PRINCIPLES OF
PHILOSOPHY
Substances, Modes,
Principle Attributes
The discussion of substance and its properties
is much more complex than the discussion of eternal truths, but once all the
terms are sorted out it is not that difficult to grasp. There are three terms
that are crucial to Descartes' understanding of basic ontology: substance,
principal attribute, and mode. A substance is just a self-subsisting thing. A
principal attribute is a special property of a substance, the property that
makes that substance the kind of substance that it is. ("Principal
attribute" is just another way of saying "essence".) A mode is
any other property of a substance.
Descartes defines a substance as a thing that
does not depend on anything else for its existence. That is to say, substance
is a self-subsisting thing. Strictly speaking, then, only God is really a
substance, because everything else depends on God for its existence (according
to Descartes' picture, not only does God initially bring us into existence, but
he must continually recreate us at every instant). More loosely speaking,
though, anything that depends only on God for its existence counts as a
substance.
The first thing to realize is that according
to Descartes there are only three substances in the world: there is God, there
is mind, and there is body. Jello is not one substance and gold another; both
are the same substance of body. Since a principal attribute is the property
that makes a substance the kind of substance that it is, there are also only
three principal attributes: we have no idea what God's principal attribute is
(if he even has one), but the principal attribute of mind is thought, and the
principal attribute of body is extension.
The second important thing to realize is that
the distinction between substance and principal attribute is only conceptual.
That is to say, we have two concepts, (i.e. "principal attribute" and
"substance") but these two concepts do not actually correspond to two
different things out in the world. There is no such thing as a substance
without its principal attribute. Body cannot exist without extension, and mind
cannot exist without thought. This makes perfect sense when you consider that
the principal attribute makes the substance what it is. How could a substance exist,
Descartes asks, without being any particular kind of thing? It is impossible.
In fact, not only can a substance not exist without its principal attribute (a
metaphysical claim), a substance cannot even be clearly conceived without its
principal attribute (an epistemological claim). How can you clearly conceive of
something without clearly conceiving what sort of thing it is? The relationship
between principal attribute and substance, then, is extraordinarily intimate.
The strong conceptual relationship between a
substance and its principal attribute is what Descartes draws on in order to
prove that the essence of mind is thought and the essence of body is extension.
The proof of these claims rests on an unstated premise: P is the essence of S,
if and only if I can conceive of S attributing only P to it. We can understand
why Descartes would feel justified in asserting this premise given the strong
conceptual relationship between a substance and its principal attribute. The
principal attribute (or essence) is just that property that allows you to
conceive of the substance. Whatever property that, all by itself, allows you to
clearly conceive of the substance, then, must necessarily be the essence of
that substance. (The full proof that thought is the essence of mind, and
extension of body, will come in the next section.)
A mode, on the other hand, is much less
intimately connected to a substance. A substance could exist without any
particular one of its modes (though it could not exist without any modes at all).
For instance, a substance could exist without being square, but it cannot exist
without being shaped. A mode is actually just a particular way of being the
principal attribute. A principal attribute is something determinable, (i.e. the
property of extension or the property of thought) and a mode is a determinate
way of being extended or thought (for instance, square is a way of being
extended and imagining a unicorn is a way of being thought).
Analysis
Descartes' analysis of substance and principal
attribute is probably the most important section of Part I. It is in defining
this terminology that he lays the groundwork for his entire physics, by
establishing the subject matter of that science. In defining physical substance
entirely in terms of extension, Descartes is ensuring that the physical
sciences can be conflated with the study of geometry. All properties of
substance can be explained simply by appealing to the properties of geometric
figures. It is in this discussion that we see Descartes at the height of his
offensive attack on Scholastic philosophers.
Like the Scholastics, Descartes claims that
substances are the most basic units of existence. Where he diverges is in
claiming, first, that there are only three substances and, second, that substances
and their essences have such a tight connection. According to the Scholastic
view there were numerous substances, all composed of various combinations of
the four elements. The essence of a substance was the property that made the
substance the sort of substance that it was, but aside from that important role
it was no different from other properties. The further properties of a
substance did not have any connection to the essence. For example, according to
the Scholastics the essence of man was his rationality. However, man could also
have qualities such as "pale" and "tall" that had nothing
to do with this essence. In addition, according to the Scholastics, substance
could survive the loss of its essence, though naturally not as that same sort
of substance. So, for instance, if a man lost his rationality he would cease to
be a man, but he would not cease to be a substance. He would just be a
different sort of substance. It is by strengthening the connection between
essence and substance that Descartes is able to so reduce the number of
substances in the world. If a substance cannot be conceived of without its
essence, there are very few candidates for essence and, correspondingly, few
for substance. The only things we cannot conceive of are the logically
impossible.
REFERENCE
Descartes, Rene. Principles
of Philosophy. Trans. Valentine Rodger Miller and Reese P. Miller.
Boston: Kluwer Academic Publishers, 1991.
Descartes, Rene. The
Philosophical Writings of Descartes. Trans. John Cottingham, Robert Stoothoff,
Dugold Murdoch. New York: Cambridge University Press, 1985.
Cottingham, John, ed. The
Cambridge Companion to Descartes. New York: Cambridge University
Press, 1992.
Des Chene, Dennis. Spitis
and Clocks: Machine and Organism in Descartes New York: Cornell
University Press, 2001.
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