Here’s a further issue for Klein’s account of useful falsehoods. For reference, here’s the full account again:
The belief that uf is a useful falsehood to S (for acquiring knowledge) by producing a
doxastically justified belief that h iff:
1. uf is false
2. The belief that uf is doxastically justified for S
3. The belief that uf is essential in the causal production of the belief that h
4. uf propositionally justifies h
5. uf entails a true proposition, t
6. t propositionally justifies h
7. Whatever doxastically justifies the belief that uf for S also propositionally
justifies t for S.
According to the above account, whatever justifies the false belief has to justify the true proposition as well, and both the true proposition and the false belief have to justify the piece of knowledge in question. Suppose we left the account there, expunging clause 5 altogether. Are there cases in which this elimination causes a problem? Another way to put this question is as follows. Klein develops his account to honor Hilpinen’s remark about being close to the truth, and alethic presupposition is one way of clarifying that idea. But why can’t being close to the truth be taken only in terms of being justified by the same evidence, both the useful falsehood and the truth that is explanatorily operative when we say why the inferred belief counts as knowledge? The idea is that the useful falsehood is close to the truth simply in virtue of being evidenced by precisely the same evidence that justifies the truth in question.
Here’s a variant of a case Matt McGrath raised in conversation. Suppose a person reasons through a false theory to a true conclusion, on the basis of evidence that actually confirms good reasons for believing the true theory. To be specific, suppose the bull in front of you is snorting and pawing the ground. Seeing this is evidence for you that he’s about to charge, and that’s evidence for you that you should get as far away as possible. The false theory in question is some animistic conception of things according to which an evil spirit has possessed the bull, and since the spirit is evil, one should get as far away as possible.
In such a case, there is no entailment relationship between the claim that the animistic claim and the claim that the bull is about to charge. Is there an epistemic relation? That is, does the belief that there is an evil spirit possessing the body of the bull justify (for the person in question) the claim that the bull is about to charge? I’m inclined to say that in some cases it will, and in some cases it won’t, but that it doesn’t much matter. If this point is correct, then a false belief can be useful for the acquisition of knowledge even if the story as to why knowledge is acquired appeals to truths that bear no logical or epistemic relation to the falsehood in question.