  Kant’s argument is particularly powerful because the assumptions on which it is built are fairly weak, indeed much weaker than they might at first appear to be. At times Kant argues that moral knowledge cannot be based on experience because it requires knowledge of absolutely universal truths that transcend all earthly experience, but this argument does not need that strong assumption. In fact, the argument would work even if (contrary to Kant) the most basic moral principle has many exceptions and is true only some of the time. Arguably we would still need to appeal to examples if we are to learn from experience when the principle applies and when it doesn’t, and then we would need some way to determine the moral status of the examples. But, again, it would be question begging to assume that knowledge of their moral status comes from experience rather than a priori, since the possibility of this is what is at issue.