actually has an explanation, for this, in effect, is to grant that the universe is rational
through and through. And this occupies almost as high an echelon in one's wish book as
does the existence of God. Hume argued that we can conceive of an uncaused event, and,
since whatever is conceivable is possible in reality, PSR is false. Bruce Reichenbach
(1972) charges that Hume confuses epistemic with ontological conditions. To be sure,
there is a distinction between what is conceivable and what could exist, the former
concerning the epistemic and the latter the ontological order. Nevertheless, Reichenbach's
rebuttal is far too facile, for it fails to face the fact that our only access to the ontological
order is through the epistemic order. The only way that we humans can go about
determining what has the possibility of existing is by appeal to what we can
end p.123
conceive to be possible. Such modal intuitions concerning what is possible are fallible;
they are only prima facie acceptable, because they are subject to defeat by subsequent
ratiocination. They are discussion beginners, not discussion enders. In philosophy we
must go with what we ultimately can make intelligible to ourselves at the end of the day,
after we have made our best philosophical efforts. What can the defender of the PSR say
to get us to give up our prima facie Humean modal intuition? Plainly, the onus is on her,
since it is she who uses the PSR as a premise in her cosmological argument.
Some cosmological arguers claim that PSR is self-evident, in the way the law of excluded
middle (that for every proposition, p, p-or-not-p) might be, and accuse those who reject it
with having a bias against theism. However, claims of self-evidence are of little use to
those who are not party to them, just as that the law of excluded middle appears self-
evident to us is of no help to those intuitionist mathematicians who do not see it this way.
Claims of self-evidence simply end discussions, and accusations of bias are a two-edged
sword.
Another way of supporting PSR is to show that it is pragmatically rational for an inquirer
to believe it, since by believing that everything has an explanation the believer becomes a
more ardent and dedicated inquirer and thus is more apt to find explanations than if she
did not believe this. This pragmatic sense of rational concerns the benefits that accrue to
the believer of the PSR proposition, as contrasted with the epistemic sense of rational that
concerns reasons directed toward supporting the truth of the proposition believed.
Because cosmological arguments attempt to establish the epistemic rationality of
believing that God exists, they cannot employ a premise that concerns only the pragmatic
rationality of believing some proposition, such as the PSR, for this would commit the
fallacy of equivocation, since “rational” would be used in both the pragmatic and the
epistemic sense. In essence, it would be arguing that it is epistemically rational to believe
a proposition p because it is pragmatically rational to believe some proposition q, from
which p follows or which is needed for the deduction of p.
A more reasonable argument for the PSR is an inductive one based on our numerous and
ever increasing successes in explaining contingently true propositions. The problem with
such an inductive argument is that there is a significant difference between the contingent
events and objects within the universe that form its inductive sample and the universe as
a whole. Thus, it is risky to infer that what holds for the former also holds for the latter.