Thursday, August 19, 2010


The folk seem to think that science can "prove" things. I used to think this just meant that they were confused about how science works. But there is a more charitable reading, which I got from a comment by Dan Johnson on prosblogion. Rather than taking the folk to be confused about how science works, we can take seriously the idea that meaning is a function of use, and take the folk to simply use the word "prove" differently from how philosophers do. The legal sense of "prove", as in "prove beyond reasonable doubt", seems to prove the point. :-) For if it is not otiose to specify that a proof is "beyond reasonable doubt", it must be possible to prove in a way that admits doubt! And hence a "proof", in the ordinary sense of the word, does not mean what philosophers and mathematicians mean by the word.


Clifton said...

It's not clear to me why the existence of the phrase "prove beyond a reasonable doubt" should be taken to suggest that there's a notion of "proof" that admits reasonable doubt. (You say simply that "it must be possible to prove in a way that admits doubt," but unless I misunderstand the otioseness argument there's a hidden "reasonable" between "admits" and "doubt.")

You might think that the phrase "beyond a reasonable doubt" is a gloss specifying what it means for something to be proved. (If I'm a judge trying to explain to a jury exactly how strong the evidence needs to be in order for them to convict, "prove beyond a reasonable doubt" may be technically redundant, but it wouldn't necessarily be otiose.) Or you might think that "beyond a reasonable doubt" is meant to distinguish the legal standard of proof for criminal trials not from a weaker standard of proof (one that admits of reasonable doubt) but rather from a stronger one (one admitting of no possibility of doubt at all, reasonable or otherwise.)

Civil trials use a weaker standard of evidence than the "beyond a reasonable doubt" standard of criminal trials -- the plaintiff simply has to show that "the preponderance of evidence" is on her side. Now, a little googling does seem to show that the act of meeting this weaker standard of evidence is referred to as a kind of proof -- "proof by preponderance of evidence" seems to be a common legal phrase.

But that's legal terminology -- it's just as technical and stipulative as philosophical terminology, so I'm not sure why we should take it as a guide to the "folk" idea of proof. And it certainly seems as though "prove beyond a reasonable doubt" resonates in the public consciousness in a way that "prove by preponderance of evidence" does not, although that may simply be because few TV shows revolve around civil trials.

I haven't actually tried it, but it seems likely to me that walking around uttering statements of the form "P has been proven and it is reasonable for one aware of that proof to doubt that P" would provoke a lot of funny looks. Although maybe that intuition stems merely from the fact that it would provoke a funny look from me, which doesn't really tell us much.

Alexander R Pruss said...

Could be. In any case, the "proofs beyond reasonable doubt" are never, or almost never, apodeictic. So even if there is no proof within reasonable doubt, my main point--that the folk need not be confused about what science does when they say that something has been "scientifically proven"--would go through.

"It's been proved that p" is an interesting locution. I think it may imply that anybody aware of that proof is in a position to know that p. Though it's a further question whether knowledge is compatible with reasonable doubt. Take: "I know that p, but from time to time I get a bit of a doubt." Is it really clear that when the speaker gets his bit of a doubt, he ceases to know that p for the time of that doubt?

Heath White said...

I think in colloquial English, "prove that p" means roughly "offer evidence that p, and p." That is, it's a success term, but the success is just the truth of what's proved, not something super-powerful about the evidence.

Alexander R Pruss said...

How about this as a rendering of "prove p": "Offer a justification for p in virtue of which p is known".

So, not just any evidence, but evidence that yields knowledge.