Descartes on knowledge in general Notes for September 13

Reasons for doubt

The first point I wanted to make was that Descartes had a special meaning for the term “doubt”. Usually, having a reason to doubt something that I believe means that I have some evidence that suggests what I believe is false.

This was the point of the examples at the beginning: I have many beliefs that are uncertain but which I have no reason to doubt. There may be no such thing as gravity, but I have no reason to doubt that it exists.** That used to say “doesn’t exist”, as in, I need a reason to believe that gravity exists. Corrected September 24.

For me, the belief that whales have a single blow hole fell into this category. When I looked at my pictures, however, I gained a reason to doubt this belief: I saw two holes!

The best way to understand Descartes is this. He resolves to doubt any belief that is not certain. It’s not that he’s looking for a reason to doubt his beliefs, in the sense I described above. It’s that he’s looking for a reason why his beliefs may not be certain. Once he finds that for a class of beliefs, he doubts all the members of that class. He does so even though he does not have what would normally be considered a reason for doubting them.

Why? He wants to find a foundation for his beliefs that will be certain. Doubting is a method, not the state he means to wind up in. He will employ the method of doubting in order to put his beliefs on a firm foundation.

Is math certain?

Descartes clearly believes that the beliefs we acquire by using our senses are not certain. But what about beliefs about numbers or geometrical shapes? He’s of two minds about them, as we will see.

On the one hand, I think he’s attracted to a point that Kimbia made. It’s possible that an evil genius has muddled my thinking even about those things.

On the other hand, I think he’s attracted to the position that Melissa, Janet, Vivian, and others were articulating. If you think you had a dream about a five sided square, you actually had a dream about a pentagon. You didn’t have a dream about a square at all, so the dream did not involve any deception about squares. You’re just confused about what you dreamed.

I’m with Descartes: both points seem to have something to them, though I don’t think they’re compatible with one another. We’ll see this again in the Third Meditation (p. 25, AT 36). It also comes up in the Fifth Meditation, though we won’t read that (see p. 46, AT 69–70).

This page was written by Michael Green for The Image of God, ID-1, Fall 2007. It was posted September 15, 2007.
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