Discourse On The Method Part IV

Overview

Descartes now turns to the meditations he performs in isolation. His first task is radical: throw away every notion, every thought, that contains even the smallest amount of doubt. But if everything he thinks could be false, there must still be some first principle that remains. He reasons that if his thoughts are being doubted, then there must be something doing the doubting. He must be something. This leads him to his famous conclusion: I think, therefore I am. This becomes the first principle of philosophy he had been seeking back in part two.

From here, Descartes establishes that the soul is distinct from the body, and in fact easier to know. We have immediate access to our thoughts, while knowledge of the body comes indirectly through the senses.

He then proposes a general rule: ideas you conceive very clearly and distinctly are true. The difficulty, of course, lies in discerning which ideas you actually conceive distinctly and which merely seem clear.

Descartes then turns to proving the existence of God. He has the idea of God, a perfect being. But where did this idea come from? An idea is the effect of something, and something less perfect cannot produce the idea of something more perfect. Therefore, God must exist as the cause of this idea. He adds that traits like doubt, sadness, and other feelings that indicate imperfection are not felt by God, and ideally should not be felt by us either. He also claims that dependence on something implies imperfection. In this way, God functions as a first principle much like certain geometrical truths serve as foundations in mathematics.

Finally, Descartes emphasizes that truth must be arrived at through reason, not through the senses. Ideas of God and the soul are intellectual, not empirical. And since God is no deceiver, all clear and distinct ideas have a foundation of truth, placed there by God himself.