Ad evidentiam itaque dicendorum sciendum est quod istius operis non est simplex sensus, ymo dici potest polysemos, hoc est plurium sensuum; nam primus sensus est qui habetur per litteram, alius est qui habetur per significata per litteram. et primus dicitur litteralis, secundus vero allegoricus, sive moralis, sive anagogicus. qui modus tractandi, ut melius pateat, potest considerari in hiis versibus: “in exitu Israel de Egipto, domus Iacob de populo barbaro, facta est Iudea sanctificatio eius, Israel potestas eius”. nam si ad litteram solam inspiciamus, significatur nobis exitus filiorum Israel de Egipto, tempore Moysis; si ad allegoriam, nobis significatur nostra redemptio facta per Christum; si ad moralem sensum, significatur nobis conversio anime de luctu et miseria peccati ad statum gratie; si ad anagogicum, significatur exitus anime sancte ab huius corruptionis servitute ad eterne glorie libertatem. et quanquam isti sensus mystici variis appellentur nominibus, generaliter omnes dici possunt allegorici, cum sint a litterali sive historiali diversi. Nam allegoria dicitur ab alleon grece, quod in Latinum dicitur alienum sive diversum.
(Dante Alighieri, Epist. 10.7)
For the elucidation, therefore, of what we have to say, it must be understood that the meaning of this work is not of one kind only; rather the work may be described as ‘polysemous’, that is, having several meanings; for the first meaning is that which is conveyed by the letter, and the next is that which is conveyed by what the letter signifies; the former of which is called literal, while the latter is called allegorical, or mystical [or moral, or anagogical]. And for the better illustration of this method of exposition we may apply it to the following verses: “When Israel went out of Egypt, the house of Jacob from a people of strange language; Judah was his sanctuary, and Israel his dominion”. For if we consider the letter alone, the thing signified to us is the going out of the children of Israel from Egypt in the time of Moses; if the allegory, our redemption through Christ is signified; if the moral sense, the conversion of the soul from the sorrow and misery of sin to a state of grace is signified; if the anagogical, the passing of the sanctified soul from the bondage of the corruption of this world to the liberty of everlasting glory is signified. And although these mystical meanings are called by various names, they may one and all in a general sense be termed allegorical, inasmuch as they are different (diversi) from the literal or historical; for the word ‘allegory’ is so called from the Greek alleon, which in Latin is alienum (‘strange’) or diversum (‘different’). (tr. Paget Toynbee)
Crambe Repetita 