Richard Swinburne has argued that the hypothesis of theism (Ill) is a very simple hypothesis. 1 Because of its simplicity Swinburne maintains that h 1 has a higher prior probability than rival hypotheses. This alleged higher prior probability is used by Swinburne in combination with other considerations to argue that h 1 has a higher a posteriori probability than its rivals.
One rival hypothesis to h 1 that is not explicitly considered by Swinburne is that there is an omniscient, omnipotent, free and perfectly evil Being. Let us call the hypothesis that such a Being exists h 2. Although Swinburne does not explicitly consider h 2 it is clear enough from what he does say that he would reject h 2 as incoherent. He maintains that an omniscient, omnipotent and free Being would have to be morally perfect. In other words, although Swinbume does not put it exactly in this way his thesis is that moral perfection is not an independent attribute of God but is derivable for His other attributes.
Presumably Swinburne's argument against h 2 would then have to proceed as follows: Since h 2 is incoherent, its prior probability is 0. Further, since no new evidence could raise the probability of a hypothesis whose prior probability is 0, the probability of h 2 will remain 0 no matter what the evidence. Therefore, the a posteriori probability ofh 2 could never equal h 1 .
In this paper I will show that Swinburne's reasons for supposing that h 2 is incoherent are mistaken. As a result, there is no reason to suppose, as Swinburne does, that h 2 is not as simple as h 1 . Consequently there is no reason to suppose that h 2 has a lower prior probability than h 1 . Ifh 2 has a higher a posteriori probability than h 2, then this would have to be shown by showing that it has greater explanatory power than h 2. Swinburne has not done this.
Swinburne's argument
Swinburne argues that "if one takes a certain view about the status of moral judgements, God's perfect goodness follows deductively from his omniscience and his perfect freedom". 2 The view Swinbume is referring to is that judgements that