The point here is that anyone who acknowledges the truth of transmitted revelation and holds that he has established its truth through reason cannot possibly oppose it on rational grounds. For him, reason is the witness to the truth of transmitted revelation. If it then testifies to its falsity, its testimony contradicts itself, and it can serve neither to establish the truth of transmitted revelation nor to oppose it.
[Objection: Attesting to the Truth of Transmitted Revelation Unless It Conflicts with Reason]
If he says, “I attest to its truth provided that it does not conflict with reason,”
[The Response on Several Grounds: The First]
the response is: This is untenable for several reasons.
First: Rational evidence establishes the Messenger’s truthfulness and the reality of what he reports without qualification. His truthfulness therefore cannot be conditional upon the absence of conflicting evidence.
[The Second]
Second: If you allow that reason might oppose transmitted revelation and demonstrate its falsity, you cannot trust any of it. Someone else’s reasoning might contain something that demonstrates its falsity. Thus, you could not have established its truth through your reason at all—yet you hold that you have established its truth through reason.
[The Third]
Third: What people derive through their reason has no limit, whether it is true or false. If someone allows that rational conclusions might contradict the Messenger’s reports, he cannot trust any of those reports. Rational conclusions that have not yet become apparent to him might contradict what the Messenger has reported.
If someone says, “I acknowledge those divine attributes that reason does not negate,” or, “I affirm those matters conveyed by transmitted revelation that reason does not contradict,” his statement has no definite bounds. For his acceptance of transmitted revelation is conditional upon the absence of an entire category of things that has neither definite bounds nor an endpoint. Whatever is conditional upon the absence of something that cannot be delimited cannot itself have definite bounds. With this principle, therefore, no faith remains.