Chapter 7 of Timothy Williamson’s “The Philosophy of Philosophy” is an extended argument against “psychologising” evidence in philosophy. Before we can evaluate those arguments, it would be useful to get clear on just what it is to psychologise evidence. In this post I’ll say a bit about what that amounts to, and in the next post look a bit more carefully at Williamson’s text to see just what position he is attributing to his opponent.
In some ways the debate Williamson is contributing to is among the oldest in modern philosophy. Consider the following two positions about perceptual evidence, each of which has found many partisans over the last few centuries.
- Perceptual Evidence is Psychological. My perceptual evidence consists in facts about the psychological states I am in when undergoing a perceptual experience. So, for instance, my perceptual evidence might include that I’m visually representing that there is a table in front of me.
- Perceptual Evidence is External. My perceptual evidence consists in facts that I perceive. So, for instance, my perceptual evidence might include that there indeed is a table in front of me.
The psychological theory has a number of advantages. It can explain how people having illusory perceptions can get the same kind of evidence (albeit of lower quality) as people having veridical experiences. It arguably staves off certain kinds of doubts about our evidence, at least to the extent that we have privileged access to our psychological states. It explains the fact (if it is a fact) that when we get evidence in favour of some proposition _p_ about the external world, we generally know what kind of evidence we have. It is unusual, that is, to get evidence that _p_, but not know whether that is visual evidence, or tactile evidence, or testimonial evidence, or whatever. If the evidence for _p_ just is the visual or tactile or testimonial experience, that is easily explained. And it offers the prospect of an easy theory of evidence possession; a point I’ll return to below.
But there’s one big cost of the psychological theory: it seems to promote scepticism. There is a long tradition, starting in the modern period with Descartes, of proponents of the psychological view wondering how to get from psychological evidence to knowledge of the external world. And there is another long tradition, culminating at the present with Williamson, of opponents of the psychological view using this worry as a reason to start with evidence in the external world, and avoid this sceptical doubt.
The debate here is not confined to perception. We can have a similar debate in testimony. Imagine I am told that _p_ by a trusted friend. I now have some evidence for _p_. What is it? One answer, similar in spirit to the psychological answer above, is that I’ve been told that _p_. Another answer, similar in spirit to the external answer, is _p_ itself. The latter answer might be favoured by a theorist of testimony who thinks that when I get testimony from a trustworthy source, I simply receive the warrant they have for believing _p_. (The two answers here aren’t quite equivalent to the positions known as reductionism and anti-reductionism in the epistemology of testimony. Someone might be an anti-reductionist and hold that the telling, rather than what’s told, is the evidence, by holding that we don’t need any extra grounds to infer, on the basis of that evidence, that _p_. I’ll say more about such inferential rules in later posts.)
Both answers here are possible, but it is much more plausible to take the evidence to be the telling rather than what’s told. So we can use that as a relatively clear example of what happens when we take evidence to be something that supports an external world proposition _p_, rather than _p_ itself. One consequence is that in reporting inferences, we can replace testimonial knowledge with knowledge that the testimony was made without making the inference worse. So imagine we know that if Celtic win today, they’re champions, and we’re told by a trusted friend that Celtic did indeed win. Then we might make either of the following inferences.
An inference from facts about football
- If Celtic won, they are champions.
- Celtic won.
- So, Celtic are champions.
An inference from facts about testimony
- If Celtic won, they are champions.
- My friend said that Celtic won.
- So, Celtic are champions.
The first is valid, while the second is not. But we are interested here in inferences, not implications, so that’s no disqualifying mark against the second inference. For the second has a virtue not shared by the first, namely that its premises are more secure. So it looks like the two inferences are equally good. And that suggests that the second inference really is just making explicit the inference that’s underlying the first.
We’ve now said enough to set up the interesting debate about philosophical evidence. Often we say things like _Intuitively, that’s a cause of that_, or _Intuitively, that’s wrong_ and so on in philosophy. What kind of evidence are we appealing to here?
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