The same applies to the signs that establish the Prophet’s prophethood, and to many reports and inferential arguments that establish particular rulings: their existence entails the validity of the ruling, but their absence does not entail its absence, since the ruling may be known through other evidence. The exception is where the evidence is necessarily entailed by what it proves; in that case, the absence of the necessary consequence entails the absence of that which entails it. When the evidence is necessarily entailed by what it proves, it can itself be proved by it, since either of two mutually entailing things can serve as evidence for the other. An example is a revelation-based ruling that can be established only through evidence from revelation: the absence of its evidence entails the absence of the ruling.

Likewise, when people have strong motives and incentives to report something, its not being reported entails its absence, while its being reported is evidence of it. If a rational consideration provides evidence for the validity of revelation, the truth of that consideration entails the validity of revelation. The validity of revelation, however, does not entail that consideration’s being true in reality.

But if we have no way of knowing the validity of revelation, we know the rational evidence that proves it; and our knowledge of that rational evidence entails our knowledge of revelation, for knowledge of the evidence entails knowledge of what it proves.

This is what is meant by saying that rational inquiry yields knowledge. There are two views concerning this entailment. According to one, it operates through a customary connection that can be broken. According to the other, it operates through an intrinsic, inseparable entailment, just as knowledge entails life, an attribute entails some subject possessing it, and the genus of accidents entails the genus of substances. For an attribute cannot exist without a subject, nor an accident without a substance.

The point here is that, if the validity of revelation can be known only through rational evidence, then