34 But, agreeing with you that in all these stories stags are spoken of instead of Iphigenias, yet, how are you sure, when you either explain or unfold these allegories, that you give the same explanations or have the same ideas which were entertained by the writers themselves in the silence of their thoughts, but expressed by words not adapted to what was meant, but to something else? You say that the falling of rain into the bosom of the earth was spoken of as the union of Jupiter and Ceres; another may both devise with greater subtlety, and conjecture with some probability, something else; a third, a fourth may do the same; and as the characteristics of the minds of the thinkers show themselves, so each thing may be explained in an infinite number of ways.
For since all that allegory, as it is called, is taken from narratives expressly made obscure, and has no certain limit within which the meaning of the story, as it is called, should be firmly fixed and unchangeable, it is open to every one to put the meaning into it which he pleases, and to assert that that has been adopted to which his thoughts and surmises led him. But this being the case, how can you obtain certainty from what is doubtful, and attach one sense only to an expression which you see to be explained in innumerable different ways?
Source: Against the Heathen (New Advent)