In recent years there’s been a lot of discussion on what is used as evidence in philosophy, but little discussion on what it means to use something as evidence in philosophy. Given how much disagreement persists on the first question, especially when it comes to the status of intuitions, perhaps we should shift our attention to the second one? And maybe this could reveal that what seems to be a disagreement is actually just a bunch of philosophers talking past each other?
A rare example of somebody who tries to be specific about using something as evidence is Nevin Climenhaga. He proposes to understand it in Bayesian terms:
E is evidence for T relative to background knowledge K iff P (TjE&K) > P(TjK) – that is, E raises the probability of T relative to K. A person takes E to be evidence for T or uses it as evidence relative to K iff his conditional credence in T given E&K is greater than his conditional credence in T given K.
This, however, strikes me as too author-oriented. First, philosophical writings are rarely framed as reports on their authors’ psychology. It is unclear how we can learn much about what philosophers would believe given that something, based on what they write. Second, on rare occasions when philosophers do comment on how their evidence influence their mental states, they don’t necessarily confirm Climenhaga’s view. Take William Lane Craig, a philosopher of religion who puts forward several arguments for the existence of God, most notably the so-called Kalam cosmological argument. Craig confesses that even if he were fully convinced that all his arguments were unsound, that wouldn’t diminish his belief in God one iota “because of the self-authenticating witness of God’s Spirit who lives within him.” Should we conclude that what Craig explicitly calls his evidence for the existence of God is not taken by him to be evidence for the existence of God? Or perhaps that he must be wrong about his own beliefs?
There are also philosophers who don’t appear to find their own arguments convincing. Take Paul Feyerabend’s remark that his case against the scientific method is only meant to “show how easy it is to lead people by the nose in a rational way.” I guess Climenhaga’s reply would be that had Feyerabend been less cynical about his own argument, the argument would have made him more likely to believe that there is no scientific method. But how can we be so sure? Moreover, some have argued that philosophers often don’t believe their more controversial claims even if take their arguments seriously and that they don’t respect their evidence the way Climenhaga suggests they do. Here’s William Lycan:
Suppose I have been thus passionately defending one of my own core philosophical doctrines, say functionalism regarding the mental. I have said in print that functionalism is a view that I would kill or die for. But now suppose I encounter an oracle who knows the truth of the matter, or perhaps God parts the clouds and tells me that in sixty seconds He will reveal whether or not functionalism is true. You invite me to bet $1,000 on functionalism. Would I take that bet? Of course not. Nor $10 for that matter. Are you nuts? This is philosophy we are talking about. In reality, I have no idea whether functionalism is true.
And here’s Keith De Rose:
Suppose I’m up on the ship of super-advanced aliens, whom I somehow (nevermind how) know to be truthful when they tell me that the issue of whether free action is compatible with determinism is one of those philosophical questions we humans puzzle over that actually does have a correct answer; that they, the aliens, actually know whether it’s compatibilism or incompatibilism that is correct; and that they will give me a chance to save the Earth and humankind by getting the question right: I get to give one answer to the question whether compatibilism or incompatibilism is true, and if I refuse to answer or get it wrong, they will destroy the Earth and everyone living there, but if I get it right, they will destroy nothing, but will return me to Earth and then peacefully leave. Or, to vary the case in a couple of different ways, suppose first that it is not the fate of the Earth and humankind that is at stake, but only my own life; or, second, that no lives are at stake and my entire encounter with the aliens is a very friendly and positive one, but that the aliens will instead give me ten million US dollars if I give the correct answer, but nothing if I’m wrong, before releasing me and peacefully leaving. In any of these cases, I’m sure I would feel very differently about the issue than I do when discussing the matter in a philosophical setting. And what’s really interesting is that, beyond the effects one would likely expect high stakes to have on the matter, at least until recently, I would have been strongly inclined to go with the opinion of the majority of philosophers, rather than my own philosophical acceptance of the matter, in these cases.
It is of course not impossible that Lycan and DeRose cannot accurately predict what they’d do in such unusual circumstances. My point is not, however, that they must be right, but rather that there is something that they use as evidence “when discussing the matter in a philosophical setting”, which is independent of how it influences their own beliefs.
In philosophy of science there’s a well-known distinction between the context of discovery and the context of justification. The former has to do with, roughly, actual thinking processes behind scientific ideas and theories, and the latter with what is used to support those ideas and theories in the scientific community. I think it might be a good idea to start making use of this distinction in metaphilosophy. I suspect the result could be that those who think that intuitions are used as evidence in philosophy are talking about evidence in the context of discovery and those who think that intuitions aren’t used as evidence in philosophy are talking about evidence in the context of justification. For example, Climenhaga points out that philosophers often believe propositions they find intuitive – but this is irrelevant in terms of philosophical justification. What matters is whether the fact that someone finds something intuitive is offered as a reason to believe it in a philosophical text (which, as far as I can tell, never happens).
Actually Climenhaga seems to some extent aware of the problem, as he mentions the difference between “private evidence” and “public evidence”. But for some reason he’s not interested, barring one footnote, in arguing that intuitions are used as public evidence, and doesn’t consider the possibility that people who he thinks he disagrees with are only talking about public evidence, which would mean that his argument largely misses the point.
Since private and public evidence seem like neat terms, why do I insist on calling it evidence in the context of discovery and evidence in the context of justification? Well, I don’t actually insist on using particular words, my point is not that metaphilosophy needs more fancy terminology, but rather rather that philosophers of science have spent some time discussing several ways of understanding the distinction since Reichenbach first introduced it in 1938, as well as arguments for doing away with it. Paying more attention to this literature sounds wiser than starting from scratch with a vague idea of the difference between what’s going on in philosophers’ minds and what’s going on in philosophical texts.
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