Theism and Explanation - Appeared-to-Blogly

136 Theism and Explanation
apparent anomaly (the existence of evil). 88 But if the theist’s defence resembled
the atomist’s spike hypothesis, its defects would be clear. The atomist apparently
has no independent reason to believe in the existence of such spikes:
his auxiliary hypothesis, as van Inwagen describes it, is entirely ad hoc. Yes,
it might be true, but we have no independent reason to accept it. 89 Pace van
Inwagen, 90 the fact that the spikes resemble the electromagnetic forces for
which we have independent evidence is neither here nor there. The point is
that van Inwagen’s ancient atomist had no independent support for this auxiliary
hypothesis. Even if his belief were true, in his situation he would have
been acting irrationally in maintaining it. A hypothesis that could be saved
from refutation only in this way lacks the virtue of simplicity. Unless it exhibits
a range of other virtues, it would be unworthy of our acceptance.
7.5 ONTOLOGICAL ECONOMY
I outlined a moment ago Richard Swinburne’s defi nition of “simplicity”
(7.4). There exists an explanatory virtue which closely resembles his conception
of simplicity, but I shall deal with it under a different heading, that
of ontological economy. This resembles the classic principle of economy-inexplanation
attributed to William of Ockham: entia non sunt multiplicanda
praeter necessitatem (entities are not to be multiplied beyond necessity).
But it is a little more specifi c, and avoids some of the diffi culties inherent
in Swinburne’s view. It is most accurately described as a principle of “ontological
type-economy,” which suggests that we should not posit new kinds
of entities without suffi cient reason. Such a principle is not unrelated to the
issue of background knowledge. When discussing background knowledge
(7.2), I argued that we would have more reason to accept a hypothesis positing
unobservable entities if we could point to familiar mechanisms that
bore some analogy to it. My principle of ontological type-economy could be
regarded as another way of expressing this idea. It suggests that we should
not posit a hitherto unknown type of cause without suffi cient reason.
Something akin to this principle appears to underlie the actualism of
Charles Lyell’s Principles of Geology 91 —the idea that “no causes whatever
have from the earliest time to which we can look back, to the present,
ever acted, but those now acting; and that they never acted with different
degrees of energy from that which they now exert.” 92 What inspired this
principle? It was, certainly, a desire to posit only verae causae of the kind
John Herschel had espoused, 93 that is to say, “causes which experience has
shown to exist, and to be effi cacious in producing similar phenomena.” 94
But underlying this vera causa principle is a desire to avoid positing new
kinds of entities when familiar ones will suffi ce. For Lyell argues that if
we abandon this actualist principle, then we open the door to “the utmost
license of conjecture in speculating on the causes of geological phenomena.”
95 The implication of Lyell’s position seems to be clear. It is better to