How to argue for pragmatic encroachment.

Purists think that changes in our practical interests can't affect our knowledge unless those changes are truth-relevant with respect to the propositions in question. Impurists disagree. They think changes in our practical interests can affect our knowledge even if those changes aren't truth-relevant with respect to the propositions in question. I argue that impurists are right, but for the wrong reasons, since impurists haven't appreciated the best argument for their own view. As I show, there is an argument for impurism sitting in plain sight that is considerably more plausible than any extant argument for impurism. [ABSTRACT FROM AUTHOR]