I've been thinking about the knowledge-action principle. I've also been thinking about whether knowledge of p's truth is sufficient for (a) p being a reason of yours and (b) p being treated by you as a reason of yours. Here's an argument. Thoughts are very much appreciated. (Context. I've been discussing the view that knowledge of p's truth suffices for p's inclusion in your evidence.)
In a similar vein, suppose we think of evidence as a reason that provides a subject with a justification for holding a belief. Some have defended the view that knowledge of p’s truth is sufficient for it to be epistemically permissible to treat p as a reason for action or including p in a piece of practical reasoning. Various arguments have been given for the view, but rather than reviewing those, let me add one of my own. Were it not permissible to treat p as a reason for action and include p in practical deliberation, there would be a conclusive reason to refrain from so doing. But, if there were a conclusive epistemic reason to refrain from including the belief that p is the case in practical deliberation, it would seem that such a reason ought to constitute a conclusive reason not to believe p in the first place. The existence of such reasons would seem to ensure that the subject could not satisfy the justification condition on having knowledge that p. Thus, it seems that the principle could admit of no counterexamples.
Now, the principle is about the permissibility of treating something as a reason rather than whether something is a reason. While this is a distinction that might matter to some, it is hard to see how someone who accepts an access principle such as AA could make use of such a distinction. For according to AA, on the hypothesis that something is a piece of evidence or a reason, the subject is in a position to know that this item is a piece of evidence or a reason. It is hard to imagine how someone might permissibly treat a non-reason as a reason when they were in a position to know that the non-reason could not be a reason. So, I have a difficult time seeing how someone who accepts AA could say that it is permissible to treat what you know as a reason for action while saying that it might nevertheless be the case that what is treated as a reason is no reason at all. It seems there is good reason to think that it is permissible to treat what you know as a reason for action. It seems that knowledge of p’s truth, then, ought to suffice for p’s inclusion in your evidence if we say that the reasons that can properly figure in practical deliberation constitute evidence for, say, beliefs about what ought to be done. The identification seems perfectly apt given the gloss on evidence as that which gives you a reason that can justify a belief.