Seriously, especially if these is an lower level philosophy class, your teacher would love to hear you critique Descartes.
Descartes was famous for a variety of things. If you've taken any mathematics, you've probably heard of a Cartesian plane and you've done some analytic geometry, both thanks to Descartes. But for your philosophy class, it is his work on the mind-body problem that is most important.
Descartes said "Cogito ergo sum", which we recognize as "I think, therefore I am." What Descartes sought to do was to discard everything which could be doubted, and arrived at one thing which he knew could not be doubted at all: his thoughts, and that he was thinking. The body seems to exist, and we perceive it through our sense, but we have known our perceptions to mislead us. However, because he has thoughts, and he knows that thoughts exist because he has them, his existence cannot be doubted. He constructed the Wax Argument. Essentially his point is that a solid piece of wax and warmed or melted wax seem to the senses to be completely different, but they are still both just wax, and so only his mind could properly deduce the nature of wax.
Later in his life, Descartes would wax poetically on the human mind with his philosophy of Dualism. According to Descartes, the body is essentially a machine that follows all laws of physics, whereas the mind is a bit supernatural. Descartes said that only humans have minds, and that the mind interacts with the body at the pineal gland (again, asserting that only humans have these), with the mind and body capable of influencing each other.
Now an important note in Descartes work was that he was a highly religious man. For this reason, he believed humans to be above all else, and we now know that humans are not the only animals to have minds or pineal glands. Also of interest, his Meditations had a rather poor ontological argument for the existence of God, on which he built a new argument saying that God would not reasonably deceive him, so his perception could now be trusted. You see the part that his beliefs played in his philosophy.
Anyways, the point here is that you can use his most famous work as a springboard for a solid rebuttal or concurrence.
