Descartes' Argument for the Existence of Material Objects

A/ The argument for the existence of material objects:

The final conclusion that Descartes makes concerning the existence of material objects is that they exist and that they are the cause of Descartes' ideas of them. This conclusion is made finally in Meditation 6. In Meditations 2 and 5, Descartes also mentions about their existence as being a suspect of truth for his investigation, and in Meditation 2, material objects are corporeal things that he can observes using senses. Thus, when he speaks about corporeal things that he perceives by senses, we know that he is talking about material objects. In addition, not only material objects are objects that Descartes perceives through senses, in Meditation 5, Descartes mentions about another kind of material objects that associate with figures, numbers, size and shape and pertain to mathematics; in other words, objects that can cause idea of them, and they are what Descartes can conceive either by himself or by means of other ideas such as mathematics. In these Meditations, Descartes already recognizes or has a feeling that they really exist, but he needs to examine more so that they can be better known; in other words, he knows that they exist, but he must prove that his knowledge of them are clearly and distincly perceptions so that he can say about the certainty of their existence. Let us look back at some statements that he writes regarding the existence of those material objects in Meditation 2 and 5. For example, in Meditation 2, Descartes says that material objects have a distinct impression on him by starting to view and to examine his own body as a material object:

But as to the body, I was not in any doubt. On the contrary, I was under
the impression that I knew its nature distinctly. (31)

For corporeal things other than his own body, Descartes says, also are more distinctly known:

But int still seems (and I cannot resist believing) that corporeal things--
who images are formed by thought, and which the senses themselves
examine-- are much more distinctly known than this mysterious "I" which
does not fall within the imagination. (32)

Finally, Descartes give out another example that he made on the wax, a natural object that he can touch and conduct an experiment to study its existence. In his observation of the wax, he finds out about its true property, one that is unchanged and remains eternally while other properties change and disappear under our senses. After this experiment about the wax, Descartes thinks that if the corporeal objects exist, he knows more clearly about them by the intellect:

It is what my imagination shows it to be: namely, that this piece of wax
can change from a round to a square shape, or from the latter to a
triangular shape? Not at all; for I grasp that the wax is capable of
innumerable changes of this sort, even though I am incapable of running
through these innumerable changes by using my imagination. Therefore
this insight is not achieved by the faculty of imagination. (32)

Even though Descartes' knowledge about the wax is gained by his reasoning, he cannot deny that the wax and its material are not in a dream or in an imagination. Finally, in Meditation 6, Descartes proves that material objects exist and that they are the cause of his ideas of them:

1) There must be some cause for my ideas of sensory things:

And since the ideas perceived by sense were much more vivid and explicit
and even, in their own way, more distinct than any of those that I deliberately
and knowingly formed through meditation or that I found impressed on my
memory, it seemed impossible that they came from myself. Thus the remaining
alternative was that they came from other things. (50)

2) This cause is either in me or outside of me:

I cannot understand them clearly and distinctly without me, that is, without a
substance endowed with understanding in which they inhere, for they include
an act of understanding in their formal concept. Thus I perceive them to be
distinguished from me as modes from a thing. I also acknowledge that there
are certain other faculties, such as those of moving from place to another, of
taking on various shapes, and so on, that, like sensing of imagining; cannot be
understood apart from some substance in which they inhere, and hence without
which they cannot exist. But it is clear that these faculties, if in fact they exist,
must be in a corporeal or extended substance, not in a substance endowed
with understanding. (50-51)

3) This cause is not in me [because I am not aware of being this cause]:

But this faculty surely cannot be in me, since it clearly presupposes no act of
understanding, and these ideas are produced without my cooperation and
often even against my will. (51)

4) This cause must therefore be outside me:

Therefore, the only alternative is that it is in some substance different from
me, containing either formally or eminently all the reality that exists objectively
in the ideas produced by that faculty, as I have just noted above. (51)

5) This external cause must be either physical bodies or God:

Hence this substance is either a body, that is, a corporeal nature, which
contains formally or eminently all the reality that exists objectively in
the ideas, or else is God. (51)

6) This cause cannot be God (for then He would be deceiving me):

But since God is not a deceiver, it is patently obvious that he does not send
me these ideas either immediately by himself, or even through the meditation
of some creature that contains the objective reality of these ideas not formally
but only eminently. For since God has given me no faculty whatsoever for
making this determination, but instead has given me a great inclination to believe
that these ideas issue from corporeal things, I fail to see how God could be
understood not to be a deceiver, if these ideas were to issue from a source
other than corporeal things. (51)

7) Therefore, the cause of my ideas of physical must be actually existing physical bodies:

For since God has given me no faculty whatsoever for making this determination,
but instead he has given me a great inclination to believe that these ideas issue
from corporeal things, I fail to see how God could be understood not to be a
deceiver, if the ideas were to issue from a source other than corporeal things.
And consequently corporeal things exist. (51)

For the proof that God is not a deceiver, the following statement of Descartes in Meditation 3 will count:

The whole force of the argument rests on the fact that I recognize that it
would be impossible for me to exist, being such as nature as I am (namely,
having in me the idea of God), unless God did in fact exists. God, I say,
that same being the idea of whom is in me: a being having all those
perfections that I cannot comprehend, but can somehow touch with my
thought, and a being subject to no defects whatever. From these
considerations it is quite obvious that he cannot be a Deceiver, for it is
manifest by the light of nature that all fraud and deception depend on
some defect. (40)

B/ How the view that Descartes articulates in Meditation 6 provides a foundation for mechanistic science:

Recall that I did mention about Descartes' example of the wax and objects that are the subjects of mathematics in Meditation 2 and 5. The special idea about how to obtain the true property of the wax using reasoning and experiment but not using senses proves that Descartes is the founder of mechanistic science or science in general because mechanistic science is the study of the relationship among size, shape, extension and motions of physical or material objects, and because when he studies about the wax, he focuses on its size, shape and its extension which are the most important things that are changing and therefore reveal the true property of it, the extension and the changing of the size and the shape of the wax. All of these things, of course, are subjects that mechanistic science use as said by the above definition. In Meditation 6, Descartes also admits the important role of the quantities rather than the qualities of material objects which include size, shape, extension -- the essential properties that can assist the creation of concepts that are used by mathematics and mechanistic sciences, and by first sensing them he can have better ideas of them.

Moreover, I also recalled that the use of the senses antedated the use of reason.
And since I saw that the ideas that I myself fashioned were not as explicit as
those that I perceived through the faculty of sense, and were for the most part
composed of parts of the latter, I easily convinced myself that I had absolutely
no idea in the intellect that I did not have beforehand in the sense faculty. (49)

Although, senses and material objects are the essential things for the observation and study of science, senses appear less precise and untrusted:

Afterwards, however, many experiences gradually weakened any faith that
I had in the senses. Towers that had seemed round from afar occasionally
appeared square at close quarters. Very large statues mounted on their
pedestals did seem large to someone looking at them from the ground level
and in countless other such instances I determined that judgments in matters
of the external senses were in error. (50)

And Descartes thinks that reasoning makes him think differently than what he perceives through senses:

As to the arguments that used to convince me of the truth of sensible things,
I found no difficulty responding to them. For since I seemed to be driven
by nature toward many things about which reason tried to dissuade me, I
did not think that I was taught by nature deserved much credence. (50)

C/ Strength and weakness of Descartes' attempt to ground science in philosophy:

1/ Strength:

* His belief in the existence of the natural objects which are the main subjects for the study of any science because science is the study of natural things-- things that exist around us.

* His great idea in finding the true properties of material objects. For example, his experiment of the wax shows that unlike other people who don't have any doubt about the senses, Descartes use his observation that assists him checking his senses such as seeing, hearing, touching, smelling ect. in discovering that all of the properties such as shape, size, color and fragrance of the wax are not permanent properties of the wax and can be changed because they all disappear when the wax is melted. Thus, Descartes has built an important foundation of mechanistic science, that is using the doubted mind -- a mind in reasoning -- to discover true properties of material objects.

* His account of using senses as the first action that scientists must use in order to study material objects is a good foundation for science because some scientists even don't use senses at all and use only imagination in establishing scientific concepts.

2/ Weakness:

* Even though Descartes uses senses as the first condition in studying material objects, he later denies senses as an important role in scientific study because he thinks that reasoning is more important. For example, he says that the extension property of the wax cannot be found without 'the doubting mind' that re-checks all the phenomena given by senses:

Not at all; for I grasp that the wax is capable of innumerable changes of this sort,
even though I am incapable of running through these innumerable changes by
using my imagination. Therefore this insight is not achieved by the faculty of
imagination. What is it to be extended? Is this thing's extension also unknown?
for it becomes greater in wax that is beginning to melt, greater in boiling wax,
and greater still as the heat is increased. And I would not judge correctly what
the wax is if I did not believe that it takes on even greater variety of dimensions
than I could ever grasp with imagination. It remains then for me to concede that
I do not grasp what this wax is throught imagination; rather, I perceive it through
the mind alone. (33)

* For the example of the wax, it is obviously that Descartes did not use his mind alone, since he couldn't obtain the extention of the wax without first doing an experiment on it. Thus, Descartes' accomplisment is not by reasoning alone but by a combination of senses and reasoning; however, his "first doubting mind" is what he acclaimed as his reasoning achievement in his succesful experiment of material objects.

* In deed, although in science and especially in mathematics, many mathematicians and physicists did come up with theories that are the results of their "first doubting mind" that something needs to be re-examined in the process, and many theories are just the result of reasons or by a priori. Morevoer, many others compiled and created scientific conceptions through observations and using senses such as Newton's theory of gravity because it is obviously that Newton couldn't come up his theory of the earth's gravity without "first seeing a falling apple or falling objects to the ground". Thus, Descartes heavy account on only reasoning is not a good ground for science.

References

Descartes, Rene. "Meditations on First Philosophy". Modern Philosophy - An Anthology of Primary Sources. Eds. Roger Ariew and Eric Watkins. Indianapolis: Hackett Publishing Company, 1998. 22-62.