At the end of the First Meditation Descartes is in a pickle. His systematic doubting has left him in a state
where he isn’t even sure that he has a body or the external world exists because he can’t know for certain
that a powerful malignant demon isn’t deceiving him about everything he thinks he knows. At the
beginning of the Second Meditation, Descartes takes his skeptical conclusion up to revision. It occurs to
him, that however powerful the demon is there is something that it cannot deceive him about. If he is
presently beset by worries about whether or not he is being deceived, then he cannot doubt that he is
thinking about something, and if he is thinking right now then it must be true that he exists. This piece of
reasoning is known as the ”cogito argument”: I think therefore I am. In other words, if you are aware of
your own consciousness, then you can’t deny that you, who are now thinking about something, exist. Even
if you try you hardest, in your yoga class maybe, to think of nothing, then as you do so you can’t deny that
you must exist in order to do so.
This argument gives Descartes a foothold. At least he knows that he exists, this much is indubitable.
Descartes’ next step is to think about what this ”I” that he cannot doubt the existence of is. He starts of by
considering comon sense answers to the the question what am I? A rational animal maybe? A living thing
with a body that moves about seeks nourishment etc. But as soon as he considers these possibilities he
realizes that he is going down the wrong track. None of these attempts will do because they assume that
we know what an animal is or that we know how a body works, which presupposes the existence of the
kinds of things he was doubtful of. Instead, since he cannot doubt the existence of his own thoughts, he
lists some of the different types of thoughts he is aware of: he doubts, he wonders about this and that, he
desires to know, he wills to get to the bottom of the questions that worry him etc. All these are types of
thinking, or mental states. He also has sense perceptions, it seems to him, or it appears to him that he sits
in a room at a table. The demon might decive him about the veracity of these impressions, maybe they are
illusionary. However, the demon cannot deceive him about the fact that it seems to him as if he is sitting in
a room etc. So, the properties that he has as a thinking thing, the mental states he is in, is something even
the demon can’t fool him about.
Descartes has know established that he can know the contents of his own mind. He know tries to show that
even the things that we think we know the most about, ordinary objects that we see everday, we really
don’t know through our senses. He pick a wax candle as his example of the kind of confused impression we
get if we only rely on our senses. If rely on what the senses tell us about the candle, then we discover that
they first tell us that the candle is hard to the touch, it makes a sound if you tap it, it smeels faintly of
beeswax, and it has a certain color and shape. However, as it burns the appearance of the candle change
dramatically, as the candle melts it changes color and shape, it becomes liquid , it smell differently etc.
However, there are certain thing about the candle, and any physical body: any chunk of matter will always
be extended in space. Anything that is extended in space retains certain geometrical properties, the shape
of the object might change but it will have some shape or other. Descartes point with this exercise is to
convince his readers that what we know for certain about the essence of material bodies we know though
the use of reason, not our senses.
So, what does Descartes know at this point? It might not seem like much, but the results quickly add up. He
has established that there are two different kinds of things in the world: mind, the kind of thinking thing he
is, and extended thing, that is matter, with different properties. Since it was possible for him to doubt the
existence of body or matter, but not to doubt the existence of a subject that is conscious of its own mental
states, he knows that these are different kinds of things that are independent of each other. Later on in the
Meditations descartes tries to show that we are born with the idea of a perfect being, but that the idea of
such a being must be caused by an actual perfect being, namely God. But since God is a perfect being, God
would not deceive us about the things we perceive clearly and distinctly, or let an evil demon get away with
deceiving us. This means that we can know that the real worl consists of pieces of matter with geometrical
propertis that our minds are capable of obtaining knowledge about. In other words, we can know about the
structure of the external world if we do mathematical physics and regard the natural world as a big
mechanical system. However, since the mind is different from matter, it’s not extended in space; and you
can’t divide it into pieces as you can with any chunk of matter. Therefore the mind, or the soul, is a
substance that can’t be destroyed the same way bodies can. This is what Descartes wants, we can believe
in the immortality (indestructability) of the soul but still analyze nature as a giant mechanical system.
Unfortunately, this way of refuting scepticism heavily relies on Descartes attempt to prove the existence of
God. If you don’t accept this argument, then Descartes might be assured of his own existence and the
content of his own thoughts, but this is not very much, for all he knows it is still possible that he is a brain in
a vat or he lives inside the Matrix. Even if you accept Descartes’ argument about the knowledge of the
external world, our knowledge is very different from our commonsense perception of the world. The real
structure of the world is revealed by mathematical physics, not the way it it looks to us from a common
sense point of view. According to Descartes, it’s the scientific image of the world that is correct, not our
ordinary perception of it.