The failure of the senses argument to conclusively prove that everything is false leads Descartes onto the dreams argument. At no point can anyone be certain whether they are awake or dreaming. This makes the dream argument more powerful than the senses, because it starts to question the fundamental qualities of things, such as colour. Furthermore, most people can relate to the unusual images produced by the world of dreams.
But the dreams argument too has its limitations. Mathematical certainties like arithmetic and geometry contain facts that are certain and indubitable. A square always has four sides even in a dream, so the dreaming argument cannot raise any doubts about this. So we have to find another argument that goes one step beyond dreams, something that allows us to question the more fundamental properties of the universe.
Descartes believes such an argument is possible. According to the malicious demon argument, an omnipotent being controls us and deliberately feeds us misleading information. We might think that two plus three equals five because the demon wants us to believe this. Even though I feel certain of the knowledge, the malicious demon again has created this idea of certainty within me. This can therefore lead us to a position of complete scepticism. If a malicious demon is controlling us, we can’t be certain of anything.
Descartes end the First Meditation at this point, which takes us to the next question: is there anything that we can be absolutely certain about? In the Second Meditation, Descartes reaches his famous conclusion about his own existence. This he cannot doubt. He is a thinking thing, able to affirm or deny something. By going through the doubting process, this in fact proves he is a thinking thing. Even if I’m doubting, I’m still thinking, which means that I do exist. No matter what the malicious demon is feeding us, we cannot doubt the fact that we think and exist. Our own existence is something we can be certain of.
What we’ve learnt from Descartes so far is that most of our ‘knowledge’ is not really knowledge at all as it’s open to doubt. The one thing we can be certain of is that the fact of our own existence. How we can therefore start with ‘I exist’ and build on top of this to obtain new knowledge? This seems fairly limited at first glance. Although we now have the foundational knowledge in place, what does Descartes propose in terms of a method? By reflecting on any subject, our certainty is based on a clear and distinct perception that cannot be doubted. This certainty has a distinct quality, so this gives him a method.
We can start with the ‘I exist’ knowledge, and then by repeatedly applying the ‘certain perception’ method, we can build further knowledge. Descartes does this through the remainder of the meditations. He can know the nature of his body and mind, for example.
The main objection is that Descartes has fallen short of proving ‘I exist’. He hasn’t done enough in the meditations to prove what an ‘I’ is? Is it some sort of ‘self’ extended through time? All that Descartes has is a thought of an ‘I’, not an ‘I’ itself. I can feel as if I doubt, but this doesn’t prove that ‘I’ exist. Once God’s existence has been established later in the meditations, Descartes is able to argue that because God is perfectly good, God would not allow us to be regularly deceived. So our perceptions must be true and we do exist.
However, can you be totally certain of any thought that you had a few seconds ago? At each individual moment of time we might be certain of a certain thought, but how do we fit all these thoughts together to create continuity through time and a sense of a person. According to Descartes, if God is incapable of deceiving us, we must be certain there is a continuation of time. We can look back and trust our previous perceptions. This then creates the sense of ‘I’.
Another common criticism of Descartes is whether he was right to demand complete certainty for our beliefs. Shouldn’t degrees of certainty be sufficient? Other theories of knowledge suggest that something is ‘knowledge’ if it is coherent and fits in consistently with other forms of knowledge. An introductory to epistemology would provide other ways to perceive knowledge, which could lead to further ways to question Descartes’ approach.
To summarise then, what we can learn about knowledge depends on which process we follow to decide what knowledge is. Is radical doubt the correct approach? Is absolute certainty the right goal to have? We rarely have absolute knowledge in real life. We have different standards depending on what we want to prove (criminal guilt or what to watch on television). So ‘knowledge’ means different things depending on the context. There are different standards. Descartes gives us a useful standard for knowledge in a particular context only. We don’t have to think this applies across the board. We learn about a very specific kind of knowledge from Descartes, which doesn’t cover knowledge in all senses.