our knowledge of the validity of revelation entails our knowledge of the rational evidence establishing it, and our knowledge of that rational evidence entails our knowledge of the validity of revelation.

The same holds for everything that can be known only through evidence. The actual existence of that rational evidence also entails the validity of revelation, but the validity of revelation does not entail the existence of that evidence.

If knowledge of the validity of revelation is necessarily entailed by knowledge of the rational evidence establishing it, and necessarily entails it, and is also necessarily entailed by the actual existence of that rational evidence—just as the actual existence of that rational evidence entails the actual validity of revelation—then it is impossible for a necessary consequence to contradict that which entails it, let alone for two mutually entailing things to conflict.

For opposing things are incompatible: the existence of either entails the absence of the other, as with contraries and contradictories.

Mutually entailing things, however, are such that the existence of either entails the existence of the other, and the absence of either entails the absence of the other. How, then, could mutually entailing things be opposing, incompatible, contradictory, or contrary?

The terms “incompatibility,” “contrariety,” “contradiction,” and “opposition” are (close in meaning) in their original linguistic usage, although their technical usages differ. Thus, contrariety always entails contradiction in the linguistic sense.

This is why linguists call either of two contraries the contradictory of the other, and every instance of opposition is