A philosophy professor of mine used to like to start a new semester by demanding of his class, “How many facts are in this room?” No right answer, of course — the lesson was supposed to be that the word “fact” doesn’t apply directly to some particular kind of thing we find lying around in the world. Indeed, one might go so far as to argue that what counts as a “fact” depends on one’s theoretical framework. (Is “spacetime is curved” a fact? What if spacetime isn’t fundamental in quantum gravity?)
Nevertheless, people sometimes use the word. A recent post by PZ reminded me of how it comes up especially in arguments over evolution, which is occasionally accused of being “just a theory.” I’ve tried to make my own view clear — when we as scientists use these words, we shouldn’t pretend they have some once-and-for-all meanings that were handed down by Francis Bacon when he was putting the finishing touches on the scientific method. Rather, we should be honest about how they are actually used. “Theory,” in particular, isn’t cleanly separate from words like “law” or “hypothesis” or “model,” and doesn’t have any well-defined status on the spectrum from obviously false to certainly true. And “fact” — well, that’s a word scientists hardly use at all. We use words like “data” or “evidence,” but the concept of a “fact” simply isn’t that useful in scientific practice.
But you know what would really be useful here? Some facts! Or at least some data. There’s one repository of professional scientific communication that I know very well — SPIRES, the high-energy physics literature database run by SLAC. (My
hypothesis guess is that any other field would turn up similar results.) I don’t know an easy way to search entire papers, but it’s child’s play to search the titles. So let’s ask it — how often do scientists (as represented by high-energy physicists) use the word “fact”?
find t fact or t facts
Okay, they clearly use the word sometimes. What about some competitors?
find t data
Ha! Now that’s the kind of word scientists like to use. And the others?
find t evidence
find t observation or t observations
You get the picture. Scientists prefer not to talk about “facts,” because it’s hard to tell what’s a fact and what isn’t. Science looks at the data, and tries to understand it in terms of hypothetical models, which rise or fall in acceptance as new data are gathered and better theories are proposed. Just for fun:
find t theory
find t model
find t hypothesis
find t law
So I’m happy to say evolution is “true,” or is “correct,” but I’ll leave “facts” to Joe Friday.