[This paper is from an epistemology anthology, and it appears to be a selection rather than the whole thing.]
The evil demon argument says that it is a logical possibility that a malicious demon exists and is causing our experiences of the external world. Therefore we cannot trust our sense perceptions (the information we receive through our senses). Since we cannot be certain that such a demon doesn’t exist, we cannot know anything that we receive through our senses. Russell’s claim isn’t that the demon is a physical possibility, nor is he claiming that the demon actually exists. Instead, his claim is that the evil demon is a logical possibility. What does he mean by this?
Moore thinks that understanding this will show us the difference between his views and Russell’s position.
The three questions that have to be answered are:
- What does it mean that this is a logical possibility?
- Is it true that it is logically possible?
- If it is true, then is it true that I cannot be certain that an evil demon isn’t causing my experiences?
First, there are three things that might be meant by saying that it is a logical possibility.
- You might say that the idea doesn’t involve a logical contradiction. But this isn’t what Russell means, because even if the idea of such a demon doesn’t involve a logical contradiction, then I can still know it to be false.
- Russell might mean that the idea of an evil demon doesn’t contradict what I already know. But that is begging the question, because the very thing I’m claiming to know is that my perception is caused by the external world, not the malicious demon, and surely that contradicts the idea of the malicious demon.
- The idea of an evil demon doesn’t contradict anything I know *immediately* or anything that is derived from immediate knowledge. Moore believes that it is likely that Russell meant this. Moore admits that he doesn’t *immediately* know that, for example, his experience of a pencil isn’t caused by the evil demon, that a certain person is conscious, or anything else logically incompatible with being caused by a evil demon. (And Moore says that some philosophers will disagree with him and Russell, and assert that one can know these things immediately.) But where Moore does differ from Russell is that he believes that, even if we don’t know something immediately, we can still be certain that an evil demon isn’t causing our experiences. “Where is Russell’s argument against this?” Moore asks.
To the best of Moore’s knowledge, Russell bases the idea that I cannot be certain of what I don’t know immeidately or of what I derive from immediate knowledge upon two ideas: (1) that what cannot be known immediately or derived from immediate knowledge must be based upon analogical or inductive arguments; and (2) we cannot be certain of what we know through analogical or inductive arguments. Moore thinks the first is true, but he doesn’t believe the second assumption. He thinks we can be certain of things known through analogical or inductive arguments.
But Moore really wants to ask Russell the following: Russell’s idea that we cannot be certain of beliefs such as “The other person is conscious” or “I hold a pencil in my hand” is based upon four assumptions:
- That I don’t know such things immediately;
- That I don’t deduce knowledge of them from things I know immediately; if both of these are true, then…
- I must know these things from analogical or inductive arguments; and
- We cannot be certain of what we know from analogical or inductive arguments.
Given this, Moore wants to ask Russell, “Are you more certain of any of these assumptions than you are that you have a pencil in your hand or that a certain person is conscious?”
Notice the strength of Moore’s reply: all four of these assumptions have to be true for Russell’s skepticism to be true. So Russell must have more evidence that all four of these assumptions are true then he has evidence that he is holding a pencil in his hand or staring at a piece of wax.
Moore is more certain that he is holding a pencil in his hand than he is of any of these assumptions, much less all of them, even though he agrees that assumptions 1-3 are true.
Moore believes that it is not reasonable to be more certain of all of those assumptions than you are that you hold a pencil in your hand or that another person is conscious. If that is true, then skepticism (at least, of this variety) has been defeated.
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