Allegory is typically defined as a descriptive or narrative literary text wherein the actions, the objects, and the characters signify ideas or concepts that lie outside the text itself. It might be seen as a kind of extended metaphor in which the literal narrative consistently parallels another level of meaning. In allegory, the writer's main interest is the abstract level of meaning, and the most common technique is the personification of those abstractions. It is thus distinguished from symbolism, in which the writer's main interest is the literal action of the story, and an object or person in the narrative suggests some meaning beyond the narrative.
While C. S. Lewis's comment in The Allegory of Love that medieval people naturally thought in allegorical terms may be an overstatement, it is certainly true that allegory was a favorite literary form of the European Middle Ages, beginning with Prudentius's fourth-century poem Psychomachia. A favorite allegorical genre was the dream vision, wherein the narrator falls asleep and has an enigmatic dream replete with personified abstractions; examples of such dream visions are the French Roman de La Rose, Gower's Vox Clamantis, and Chaucer's Parliament of Fowls. Sustained allegory also became popular in the morality play genre of the late Middle Ages, with plays like Everyman. Like many allegories, Everyman manifests a simple and unambiguous relationship between two clear levels of meaning. Other texts, notably Langland's Piers Plowman, consist of complex allegory on several levels.
Allegory was an important tool in medieval biblical exegesis (or scriptural interpretation), in which the habit of reading the Old Testament to find foreshadowings of the New became commonplace, and began to be imitated by readers of literary texts and by writers composing those texts. Beginning in the fourth century, developed by John Cassian and promoted by St. Augustine, a fourfold method of scriptural analysis was developed consisting of a literal or historical level and three allegorical or “spiritual” levels: A typological level by which the Old Testament events prefigured those of the New Testament; a moral (or “tropological”) level in which the events of the narrative were applied to private individual spiritual lives; and the anagogical level, in which the narrative was related to the fate of the soul after death. Such readings influenced creative writers, most especially Dante, who makes the point (in his famous Letter to Can Grande) that he expected his Divine Comedy to be read and interpreted as the Scriptures were—on all four levels. Ultimately, the ability to read allegorically is essential to reading medieval literature effectively.