In his sermon Christus unus omnium magister (“Christ Alone the Teacher of All”), Bonaventure treats knowledge as triplex, as threefold. There is a knowledge that belongs to faith, a knowledge that belongs to reason, and a knowledge that belongs to contemplation. These three correspond to Christ’s affirmation of himself as “the way, the truth, and the life.”
What are the source(s) of cognitio creditiva, the knowledge of faith? Bonaventure writes:
Christus namque secundum quod via est magister et principium cognitionis, quae est per fidem. Haec enim cognitio duplici via habetur, videlicet per revelationem et per auctoritatem. Sicut enim dicit Augustinus in libro de Utilitate credendi: “Quod intelligimus, debemus rationi, quod credimus, auctoritati.”
Christ, indeed, in so far as he is the Way, is the teacher and first principle of the knowledge that is by faith. For this knowledge is maintained by a twofold way, namely, through revelation and authority. For as Augustine says in his book On the Usefulness of Believing: “What we understand, we owe to reason; what we believe, we owe to authority.” 1
At this point, one might think that Bonaventure advocates here a two-source manner (rather than “twofold way”) of arriving at the knowledge of faith: one that comes by “revelation” (say, the Bible) and one that comes by “authority” (say, the church). But that is not the case. The latter, “authority,” is in fact dependent on the former, “revelation”–and this because “authority” cannot rest upon an act of the human will, but must be founded upon God’s own prior action.
Auctoritas autem non esset, nisi revelatio praecessisset; propter quod secundae Petri primo: Habemus firmiorem propheticum sermonem, cui bene facitis attendentes quasi lucernae luncenti in caliginoso loco. In quo insinuat auctoritatem sermonis prophetici, et rationem huius subiungit: Non enim voluntate humana allata est aliquando prophetia, sed Spiritu sancto inspirati locuti sunt sancti Dei homines.–Cum igitur his duabus viis contingat devenire ad cognitionem fidelem, hoc non potest esse nisi per Christum datorem, qui est principium omnis revelationis secundum adventum sui in mentem, et firmamentum omnis auctoritatis secundum adventum sui in carnem.
Authority would not exist, however, unless revelation had preceded it. Because of this, [we read] in 2 Peter 1: “We have firmer prophetic speech, to which you do well to attend, as if to a lamp shining in a foggy place.” In this [remark], he penetrates to the authority of prophetic speech, and he adds its reason: “For no prophecy was ever produced by human will, but holy men of God, inspired by the Holy Spirit, spoke.”–Since, therefore, arrival at the knowledge of faith occurs by these two ways, this is not able to occur except through Christ the giver, who is the first principle of all revelation according to his advent in the mind, and the firmament of all authority according to his advent in the flesh.