In arriving at the relevant theory about the specifics of our faculty of vision we will presumably use our eyes to gather relevant data. Based on such data we come to know about the optic nerve, the structure of our eyes, the rods and cones, etc., so as to explain how it is that vision gives us reliable access to the shapes and colors of objects around us. In reliably arriving at that theory we thus exercise the very faculty whose reliability is explained by the theory. There is no vice in this sort of circularity.
Ernest SosaThe data on which philosophical theorizing is based are rather the intuited contents themselves, concerning the various thought experiments. At least that is so outside the epistemology of the a priori.
Ernest SosaSince human good is what humans ought to pursue, the pursuit of interest to Aristotle is then such activity of soul, that which constitutes human good, namely activity that attains desiderata, where the attainment is in accord with virtue.
Ernest SosaCompare the credit for a football touchdown, which might be shared by the receiver not only with the quarterback, but also with the linesmen who make crucial protective plays, etc. The success of the touchdown play depends on the receiver, it is true; but in a particular case it might depend far more on the work of others.
Ernest Sosa