Adams's Thesis has won many people's agreement:
An indicative conditional p-->q is assertable if and only if q is high probable given p.
Or, an alternative version:
An indicative conditional p-->q is assertable to the degree that q is probable given p.
The alternative version is clearly false. When the probability of q given p is lower than .5, p-->q is hardly assertable.
But the original version is also faced with counterexamples:
E.g., There are ten balls in a non-transparent bag. You have the opportunity to pick one ball out of it. It is known that nine of the balls are black and the other one white. Let p be 'you pick a ball out of the bag', and q be 'the ball you pick will be black'. The probability of q given p is .9, which means that q is highly probable given p. But p-->q is not assertable.
So neither version of Adams' Thesis works. But there does seem to be something intuitively right in it, although it is hard to describe it. How are we going to revise and save Adams' Thesis?
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You have a definition of "Assertable"? How strong you want its modal force to be?
ReplyDeleteAnd if I change your counterexample a little bit, say, you know there are 1000 balls in the bag, and only one of them is white, the other ones black.Is it now assertable that p--〉q?