Didascalicon, Book VI: how Scripture is to be read
Chapter VIII. On the order of exposition
Exposition contains three things: the letter, the sense, the sentence. In every narration there is the letter. For the very words are also letters, but the sense and the sentence are not found together in every narration. Some has the letter and the sense only. Some has the letter and the sentence only. Some contains all three together. Every narration, however, must have at least two. That narration has the letter and the sense only where through the very utterance something is so openly signified that nothing else is left to be understood beneath. That has the letter and the sentence only where from the pronouncement alone the hearer can conceive nothing unless an exposition is added. That has the sense and the sentence where something is openly signified and something else is left to be understood, which is not opened by exposition.