Atheism and Theism 125it becomes clear that this invites questions in search of explanations by refer-
ence to antecedent causes. In short, to the extent that Hume’s remarks lead
in any direction it is towards and not away from the principle of sufficient
reason.
A different argument to a more restricted conclusion is that based on
aspects of contemporary physics. Earlier I mentioned the many-universe
hypothesis in quantum theory which arose as an attempt to overcome the
appearance of indeterminacy. This is one of a number of such efforts but many
theorists prefer to accept that quantum phenomena may be indeterminate.
Events such as the decay of a nucleus at one moment rather than another, the
emission of a sub-atomic particle or its disappearance and reappearance else-
where, may be such as could not be predicted even in principle, and hence not
such as can be fully explained after the fact by citing antecedent causes.
One response is to suggest that this kind of indeterminacy resides only at
the quantum level and that ‘ordinary’ objects and events, from the falling of
an apple to the collision of planets, are deterministic and hence are not at
odds with the principle. This is unsatisfactory for two reasons. First, by
allowing that there are or may be contexts in which it fails one concedes the
point to the objector. Even if it is not false everywhere, the fact that it is or
may be false somewhere debars appeal to sufficient reason as excluding brute
contingency anywhere. Moreover, it is likely that indeterminacy could be fed
into cosmology as a part of the story of the development of the macroscopic
world, offering the prospect of causal series leading back to events of sorts that
have been granted to be without cause. Second, and more significantly, the
response assumes in common with the objector that the principle is equival-
ent to that of universal causal determinism. This I dispute. To begin with
I believe that human actions fall within the scope of the principle, while also
believing, unlike Smart, that free action is incompatible with complete determi-
nism and that there is free action. More generally, indeterministic phenomena
- including quantum events – call for and are often given explanations.
I shall return to the issue of free action later; however, the general point
I am concerned with is that not all causal explanations are deterministic.
(Indeed given the causal pluralism sketched earlier neither are they all explana-
tions by reference to efficient causation.) Consider again the examples from
fundamental physics. Suppose there is an experimental set-up (designed to
reproduce types of events that also occur naturally) in which a radioactive
source emits particles. Let us say that the frequency and the behaviour of the
emissions exhibit quantum indeterminacy. What this is taken to imply is that
if it is asked ‘why did this happen just then, and not at another moment?’, or
‘why did the particle take that course and not another?’ there may not be an
answer – there may not be ‘sufficient reason’ in the antecedents for just that
occurrence,ex hypothesi another would have been compatible with them.