Actual Possibilities, by Jonny Blamey
Enough preamble. Here are two arguments that I take to be both modal and valid, but that seem to be about about the actual world and notabout possible worlds at all but . Neither are they about epistemic modals given the wonderful principle laid out by Moritz Schulz in this blog: (MIGHT c(might x) = 1 if c(X) > 0.)
POSITIVE MODAL ARGUMENT:
Premise: If John had set his alarm for eight o’clock he would have got here on time.
Premise: John could have set his alarm for eight o’clock.
Conclusion: John could have got here on time.
The conclusion is modal. We are to assume that in fact John did not get here on time. It is not consistent with our evidence that John got here on time, so this is not epistemic possibility. The probability that John got here on time is 0. So according to MIGHT it is not true that John might have got here on time. However, there is surely a possible world where John got here on time whether he set his alarm clock or not. But the conclusion of this argument is not trivially true. The second premise is necessary for the conclusion to follow.
NEGATIVE MODAL ARGUMENT.
Premise: The only way that John could have got here on time would have been by car.
Premise: John does not have a car.
Conclusion: John could not have got here on time.
This time the conclusion is not counterfactual, since it is assumed that John did not get here on time. So the probability that John did not get here on time is 1. We again are not using epistemic modals here since according to MIGHT John must have got here on time and the conclusion is redundant. In this second argument, the second premise must be true in the actual world for the argument to go through. Are there possible worlds in which John has a car? In these worlds he could have got here on time. But we know that in this world he doesn’t have a car, so in this world he couldn’t have got here on time.
These modal arguments are important, especially in assessing culpability, but also in improving design and assessing scientific evidence. But they don’t seem to fit either metaphysical modality nor epistemic modality.