Sylvester Mauro, S.J. (1619 1687) noted that human intellects can grasp what is, what is not, what can be, and what cannot be. The first principle, "it is not possible that the same thing simultaneously be and not be," involves them all. On the Borders of Being and Knowing begins with Greeks distinguishing being from something and proceeds to the late Scholastic doctrine of supertranscendental being, which embraces both. On the way is Aristotle's distinction between being as being and being as true and his extension of the latter to include impossible objects. The Stoics will see...