Anselm’s Theology of the Possible, part 19
The Reformed apologist and theologian Cornelius Van Til once remarked that “The Bible is … authoritative on everything of which it speaks. Moreover, it speaks of everything.” In saying this, however, Van Til was merely echoing St. Anselm, who in his treatise On the Harmony of God’s Foreknowledge, Predestination, and Grace with Free Choice (De concordia), offers this little gem on Scripture’s authority over reason:
Even if by reason we say something that we cannot point to explicitly in Scripture, or prove from what Scripture says, it is by Scripture that we know whether we should accept or reject it. For if it is a conclusion of straightforward reasoning and does not contradict anything in Scripture (since just as Scripture opposes no truth so too it gives aid to no falsehood), we accept that conclusion on the authority of Scripture precisely because Scripture does not deny what is being said according to reason. But if Scripture is unmistakably opposed to our opinion, then even if our reasoning seems unassailable to us, we must not think it is supported by the truth in any way. And so it is in this way that Holy Scripture contains the authority of every conclusion of reason: by either explicitly affirming it or in no way denying it. (De concordia 3.6)
In terms of an Anselmian theology of the possible, we may say that it is Scripture that is “reason’s possibility,” the possibility that is reason.