Quote of the Day

Scriven speaks of obligations, duties, with respect to belief: in the absence of evidence, he says, atheism is obligatory. What sorts of principles of epistemic obligation underlie this claim? Obviously we cannot sensibly hold that for any proposition A, if S has no evidence for A, then S is rationally obliged to believe ~A; for then if S has no evidence for A and also none for ~A, S will be obliged to believe both A and ~A. Some of what Scriven says suggests that it is just existential propositions with respect to which S is obliged to toe this very demanding line.

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Scriven believes that positive existential hypotheses have a very different standing from negative existential hypotheses. In the absence of evidence, he seems to think, one is obliged to believe the denial of a positive existential hypothesis, whereas of course the same does not hold for negative existential hypotheses. It is hard to see any reason for thus discriminating against positive existential hypotheses -- why should they be thought of as less credible, ab initio, than negative existential hypotheses? Indeed, according to Carnap and many of his followers, universal propositions have an a priori probability of zero; since the negative existential ~(∃x)Fx is equivalent to a universal proposition ((x)~Fx), it too would have an a priori probability of zero, so that its positive existential denial would have an a priori probability of 1. Now it is no doubt a bit excessive to claim that the a priori credibility of positive existential propositions is 1, but is there any reason to suppose that in the absence of evidence either way, negative existentials have a stronger claim on us that positive existentials? It is at the least very hard to see what such reason might be.

In any event Scriven's suggestion is entirely unsuccessful. Consider

(12) There is at least one human being that was not created by God.

It is a necessary truth that

(13) If God exists, then God has created all the human beings there are.

(If you think (13) is not necessary, then replace "God" in (12) and (13) by "the being who is identical with God and has created all the human beings there are.") (12) is a positive existential proposition; hence on Scriven's suggestion we ought to believe its denial unless we have evidence for it. Hence if the arguments for (12) fail, we should accept its denial. But any argument for (12), given the necessity of (13), can be transformed into an argument for the nonexistence of God -- an argument which is successful if the original argument for (11) ["God does not exist"] is. So if the arguments for the nonexistence of God fail, then so do the arguments for (12). But, by Scriven's principle, if the arguments for (12) fail, we are rationally obliged to believe its denial, that is,

(14) Every human being has been created by God.

On this principle, therefore, if the arguments against the existence of God fail, we are rationally obliged to believe that every human being has been created by God; and if both the arguments for and the arguments against the existence of God fail, then we are obliged to believe both that God does not exist and that we have all been created by him. No doubt Scriven would view this as an unsatisfactory result.

Alvin Plantinga
"Reason and Belief in God" in
Faith and Rationality: Reason and Belief in God
edited by Alvin Plantinga and Nicholas Wolterstorff

Jim's comments: I have some comments on this but I'll add them later.