“Now of this subject matter Divine Scripture treats according to a threefold sense: that is according to history, allegory, and tropology. History is the narration of events, which is contained in the first meaning of the letter; we have allegory when, through what is is said to have been done, something else is signified as done either in the past present or in the future; we have tropology when through what is said to have been done, it is signified that something ought to be done.”
¬ Hugh of St. Victor, “De Sacramentis,” Prologue IV.
The Anglican Breviary 