On Christian Doctrine 111The Knowledge of Tropes is Necessary.

40. Moreover, I would have learned men to know that the authors of our Scriptures use all those forms of expression which grammarians call by the Greek name tropes, and use them more freely and in greater variety than people who are unacquainted with the Scriptures, and have learnt these figures of speech from other writings, can imagine or believe. Nevertheless those who know these tropes recognize them in Scripture, and are very much assisted by their knowledge of them in understanding Scripture. But this is not the place to teach them to the illiterate, lest it might seem that I was teaching grammar. I certainly advise, however, that they be learnt elsewhere, although indeed I have already given that advice above, in the second book--namely, where I treated of the necessary knowledge of languages. For the written characters from which grammar itself gets its name (the Greek name for letters being grammata are the signs of sounds made by the articulate voice with which we speak. Now of some of these figures of speech we find in Scripture not only examples (which we have of them all), but the very names as well: for instance, allegory, enigma, and parable. However, nearly all these tropes which are said to be learnt as a matter of liberal education are found even in the ordinary speech of men who have learnt no grammar, but are content to use the vulgar idiom. For who does not say, "So may you flourish?" And this is the figure of speech called metaphor. Who does not speak of a fish-pond in which there is no fish, which was not made for fish, and yet gets its name from fish? And this is the figure called catachresis.

41. It would be tedious to go over all the rest in this way; for the speech of the vulgar makes use of them all, even of those more curious figures which mean the very opposite of what they say, as for example, those called irony and antiphrasis. Now in irony we indicate by the tone of voice the meaning we desire to convey; as when we say to a man who is behaving badly, "You are doing well." But it is not by the tone of voice that we make an antiphrasis to indicate the opposite of what the words convey; but either the words in which it is expressed are used in the opposite of their etymological sense, as a grove is called lucus from its want of light; or it is customary to use a certain form of expression, although it puts yes for no by a law of contraries, as when we ask in a place for what is not there, and get the answer, "There is plenty;" or we add words that make it plain we mean the opposite of what we say, as in the expression, "Beware of him, for he is a good man." And what illiterate man is there that does not use such expressions, although he knows nothing at all about either the nature or the names of these figures of speech? And yet the knowledge of these is necessary for clearing up the difficulties of Scripture; because when the words taken literally give an absurd meaning, we ought forthwith to inquire whether they may not be used in this or that figurative sense which we are unacquainted with; and in this way many obscure passages have had light thrown upon them.