198 ARGUMENTS: MONOTHEISTIC CONCEPTIONSCosmological argument, stage three
9 If some existential proposition concerning something whose existence
it is logically impossible to explain, and whose existence can explain
the existence of things whose existence it is logically possible to
explain, is true, then something exists whose existence it is logically
impossible to explain and whose existence can explain the existence of
things whose existence it is logically possible to explain.
10 Something exists whose existence it is logically impossible to explain
and whose existence can explain the existence of things whose
existence it is logically possible to explain (from 8, 9).
Premises 8 and 9 entail step 10, and premise 9 is, I take it, a necessary truth.
So stage three succeeds. The conclusion thus far – Something exists whose
existence it is logically impossible to explain and whose existence can
explain the existence of things whose existence it is logically possible to
explain – is interesting all by itself. The crucial premise is the first:
If it is logically possible that the truth of a logically contingent
existential proposition be explained, then there actually is an ex-
planation of its truth (whether we know what it is or not).Premise 1 is a version of the Principle of Sufficient Reason. Call it PSR.
Suppose one claims the truth of every logically contingent proposition
has an explanation, and that it cannot be the case that the truth of every
logically contingent proposition is explicable by reference to the truth of
other logically contingent propositions. Then one will be claiming that
there is some logically contingent proposition whose truth is explicable by
reference to some true but not logically contingent proposition – some
logically necessary truth. If P’s truth explains Q’s truth entails P entails Q,
then one is claiming that a necessary truth entails a logically contingent
truth. This is necessarily false – if Q is a logically contingent proposition, it
is possibly false. No necessary truth is possibly false. Were a necessary
truth to entail a logically contingent proposition, then it would be possibly
false. Hence no necessary truth can entail a logically contingent
proposition. If there are any true logically contingent propositions – and
there plainly are – then either every one of them is explicably true by
reference to some other, whose truth is explicable by reference to some
other, and so on, or some among them are true but their truth cannot be
explained. PSR is compatible with all this. It requires no attempt to
explain contingent propositions only by reference to necessary truths, and