Sam Cole, one of the students in my upper level metaphysics class, wrote an interesting paper (I am writing this with his permission) where he argued that if we do not accept the Principle of Sufficient Reason (PSR), then the following question will be unanswerable:
- Under what circumstances should we accept a given explanatory hypothesis instead of the hypothesis that the phenomenon in question simply has no explanation?
I think this is a really neat question. We have some idea of the sorts of criteria we employ in choosing between alternate explanatory hypotheses: simplicity, prior probability (perhaps I repeat myself), etc. But if we do not accept the PSR, then the no-explanation hypothesis is going to be, presumably, always available. On what grounds do we judge between our best explanatory hypothesis and the no-explanation hypothesis?
It is tempting to say: If the best explanatory hypothesis is pretty good, then we go for it. But the evaluation of the quality of hypotheses seems to be innately comparative. So this "pretty good" does not seem like it should be absolute. But if it is relative, then what is it relative to? If it is relative to other explanatory hypotheses, then its being "pretty good" seems irrelevant when comparing it against the no-explanation hypothesis. The hypothesis that JFK was shot by a bunch of gorillas escaped from the zoo is pretty good as compared to the hypothesis that JFK was killed by a rifle-toting clam, but that is irrelevant when we compare the gorilla hypothesis to the Oswald hypothesis. So what we need to know is whether the explanatory hypothesis is "pretty good" as compared to the no-explanation hypothesis. But we have no criteria for that sort of comparison!
Another tempting suggestion is this: Whenever any narrowly logically coherent explanation has been offered (asking for more than that may run into Kripkean problems), we should reject the no-explanation hypothesis. This is a more promising answer to (1). Note, however, that an opponent of the PSR who takes this route cannot oppose the use of the PSR in the Cosmological Argument. For in the context of the Cosmological Argument, the PSR is employed to claim the existence of explanations for phenomena for which narrowly logically coherent explanations—namely, theistic ones—have indeed been offered.