Back when I was a graduate student, I learned explicitly from Nagel's The Possibility of Altruism that states of myself that are worth promoting (respectively, avoiding) are worth promoting (avoiding) as found in others, and for the same reason. This simple fact, the implicit grasp of which is largely constitutive of our moral maturation, has a rather important consequence:
- If my own belief that p is something that is worth my promoting, then your belief that p is something that is worth my promoting as well, and for the same reason.
But (1) also has a very interesting theoretical consequence. My reason for promoting my belief that p is no different in kind from my reason for promoting your belief that p. But my reason for promoting my belief that p may well be what is normally considered a purely epistemic reason. Now, it is clear that I need not have a purely epistemic reason to promote someone else's belief that p (sometimes her believing p will help me epistemically, because she will use her intellect to help me; but this need not be the case). There will be cases where the only reason I have to promote someone else's belief that p is a moral reason, grounded in the value of the other's possession of the truth. But by (1), the reason for my promoting my own belief that p must then be of the same sort, namely moral or prudential. And indeed, moral, because prudential reasons are just a special case of moral reasons where the beneficiary is ourselves; the lesson of Nagel is that there is no difference between the two qua reasons. Because we can always tweak a case so that I derive no epistemic benefit from your believing p, it follows that I only have a moral or a prudential reason to promote my believing that p.
It follows from the above argument that epistemic reasons are a species of moral/prudential reasons.
However, there is a powerful objection. It could be granted that reasons to promote or bring about a belief in oneself are always moral/prudential. However, one might object that epistemic reasons are not reasons to promote or bring about a belief in oneself. Beliefs are not something one brings about in oneself—they are something one catches, like a cold, as the phrase goes.
This objection is mistaken. Sometimes when we see the overwhelming evidence for p, we immediately believe p. But sometimes we suffer from doxastic akrasia, and we need to push ourselves to believe—e.g., by forcing ourselves to think p, against long-standing habit. And while this may not be the normal case, it is very plausible that if R is an epistemic reason for my believing p, then R is a reason to promote my belief that p.
Moreover, we can imagine a scenario where my brain is so constructed that to come to believe anything that I previously disbelieved, I need to entertain the belief while stomping my left foot. And were my brain so constructed, the epistemic reasons would be reasons for entertaining-plus-stomping actions.