Does one say "allegory for" or "allegory of"?

Solution 1:

Allegory of seems to be overwhelmingly favored over allegory for, per this Ngram. The Ngram utility does not allow my attempted comparison of “Pilgrim’s Progress is an allegory for/of,” but with the “Pilgrim’s” removed it showed no hits at all for the for option and some for the of option. Trials of “read/interpreted as an allegory of/for” also showed strong preference for of.

Solution 2:

There are two ways to refer to an allegory. One is the title of it, which refers to the literal elements in the story, as "the allegory of the Cave" , as cited in the Wikipedia article you mentioned. The other way to refer to it is in regard to the things it symbolizes. In that sense, one uses "for" , e.g. It is an allegory for human self-centeredness. The syntax works the same for "parable".

Answer given by Brian Hitchcock (in the comments, but with a technical problem making it an answer).