The Middle Ages
The institutionalization of Christianity required the preservation of classical learning, including Greco-Roman ideas of metaphor. However as Erich Auerbach points out in Mimesis: The Representation of Reality in Western Literature (1968), the passage from classical to Christian civilization involved a radical change in the context within which figured language was understood. Because the classical system depended upon a precise delineation and separation of elements, Auerbach sums up its emphasis as "aesthetico-stylistic." In contrast, the Christian "ethico-theological" emphasis assumes the merging of hitherto distinct styles and foregrounds a decidedly un-Roman urgency concerning interpretation. To the early Christian fathers, figured language represented a formidable theological problem. The scriptures contain many figures and ambiguities, and Christ often chooses to teach through metaphor and parables—but the classical technology of eloquence (particularly how it defines and achieves the high style, language that moves the audience to action) is pagan and elite, neither holy nor humble.
In line with the classical tradition, which he resourcefully defends throughout De doctrina christiana (396–426; On Christian doctrine) as being essential for proper scriptural interpretation, Augustine (354–430) discusses metaphor as a trope. It is, however, how he defines a sign that clearly indicates the Christian break from the past: "A sign is a thing which, over and above the impression it makes on the senses, causes something else to come into the mind as a consequence of itself" (p. 535). For Augustine, words (the most important human signs) have an intrinsic power that may exceed the limits erected by the classical doctrine of mimetic fidelity and enforced by the Greco-Roman insistence on decorum. Augustine's view of words as signs helps him to renew and meld the two aspects of metaphor that Aristotle delineated and his classical inheritors further isolated from each other.