We talked about two things. First, what does Descartes’s method of doubt involve? Second, did he set the standard for knowledge too high?
The method of doubt is used to find beliefs that can serve as a foundation for knowledge. Only beliefs that are certain, immune from doubt, can perform this function. Descartes argued that what we believe on the basis of the senses cannot meet the standard. Consequently, he concluded, we do not know anything on the basis of our senses.
Descartes himself did not rest with this conclusion. He thought it showed that we could not know anything on the basis of the senses alone. Reason did the heavy lifting for him. But I’ll leave that for the next installment.
Descartes subjects our beliefs to doubt. What does that mean? It does not mean that he gives us reason for believing things that are incompatible with the beliefs we currently have. He does not maintain that he has evidence that he is asleep or that there is an evil demon messing with his head.
The method of doubt is more indirect. It involves two steps:
For example, suppose I believe there is a tree outside my window because I see a tree outside my window. According to the assumption, I would have to know that I’m not dreaming about seeing a tree in order to know that there is a tree because I see a tree. If I were dreaming, then I would not be seeing a tree (or anything at all) and so my seeing a tree could not be the basis for my knowing that there is a tree.
The argument for the claim is that I cannot distinguish between the truth and falsity of the scenarios. For instance, I cannot distinguish between seeing the world and having an exceptionally realistic dream of seeing the world. If I cannot tell the difference, then I cannot know whether I am seeing things or having an exceptionally realistic dream of seeing them.
We talked about an objection to Descartes’s dream argument. The objection holds that the claim is false or, at least, that Descartes had not proven it. According to the objection, while I might not be able to tell the difference between dreaming and having real experiences while I am asleep, I can tell the difference while I’m awake. If so, the claim that I cannot distinguish between dreaming and really seeing things is false. Here is Thomas Hobbes, Descartes’s contemporary.
The imaginations of them that sleep are those we call dreams. And these also, as all other imaginations, have been before, either totally or by parcels, in the sense. And because in sense, the brain and nerves, which are the necessary organs of sense, are so benumbed in sleep, as not easily to be moved by the action of external objects, there can happen in sleep no imagination, and therefore no dream, but what proceeds from the agitation of the inward parts of man’s body; which inward parts, for the connexion they have with the brain, and other organs, when they be distempered, do keep the same in motion; whereby the imaginations there formerly made, appear as if a man were waking; saving that the organs of sense being now benumbed, so as there is no new object, which can master and obscure them with a more vigorous impression, a dream must needs be more clear, in this silence of sense, than our waking thoughts. And hence it cometh to pass, that it is a hard matter, and by many thought impossible, to distinguish exactly between sense and dreaming. For my part, when I consider that in dreams I do not often nor constantly think of the same persons, places, objects, and actions, that I do waking; nor remember so long a train of coherent thoughts, dreaming, as at other times; and because waking I often observe the absurdity of dreams, but never dream of the absurdities of my waking thoughts; I am well satisfied, that being awake, I know I dream not, though when I dream I think myself awake.** Thomas Hobbes, Leviathan (1651), ch. 2.
We were divided over whether Hobbes’s objection worked or not. On the one hand, Kyle and others thought that Descartes has a good reply: you can’t tell the difference between having a particularly vivid (and dull) dream and being awake. If so, you can’t know that you’re awake and, if you can’t know that, you can’t know that you can tell that you’re in a position to know that you aren’t dreaming. Others, such as Nick and Richard (I think), were inclined to agree with Hobbes.
It may not matter much in the end. As Zach pointed out, there’s always the evil deceiver in the background, ready to fill in if the dream argument falters.
On the one hand, it seems that it is. We don’t normally require that people be able to eliminate all incompatible possibilities in order to claim to know things. It would be extraordinarily tedious of you to insist on that standard in everyday conversation.
On the other hand, Descartes’s standard seems to be just a general application of a perfectly ordinary, sensible standard for knowledge. This was the point of the example of the yellow bird.
Suppose I see a yellow bird and conclude that I know it is a goldfinch. Suppose that I do not know that it is not some other kind of yellow bird, such as a canary or a yellow-tailed Oriole. Most of us will conclude that I don’t really know it is goldfinch. Descartes’s assumption appears to explain why: I don’t know that the various possibilities incompatible with my knowing it is a goldfinch are not true.
What is disconcerting about Descartes’s argument is that it takes this perfectly normal standard for knowledge and shows that it leads to the quite extraordinary conclusion that we know nothing at all on the basis of the senses.