There is a great difference, whether the poet seeks the particular for the sake of the general or sees the general in the particular. From the former procedure there ensues allegory, in which the particular serves only as illustration, as example of the general. The latter procedure, however, is genuinely the nature of poetry; it expresses something particular, without thinking of the general or pointing to it.
Allegory transforms the phenomenon into a concept, the concept into an image, but in such a way that the concept always remains bounded in the image, and is entirely to be kept and held in it, and to be expressed by it.
Symbolism . . . transforms the phenomenon into idea, the idea into an image, and in such a way that the idea remains always infinitely active and unapproachable in the image, and even if expressed in all languages, still would remain inexpressible.
--Goethe, Maxims and Reflections