A symbol is indeed the only possible expression of some invisible essence, a transparent lamp about a spiritual flame; while allegory is one of many possible representations of an embodied thing, or familiar principle, and belongs to fancy and not to imagination: the one is a revelation, the other an amusement.
William Butler YeatsI have found nothing half so good / As my long-planned half solitude, / Where I can sit up half the night / With some friend that has the wit.
William Butler YeatsFair and foul are near of kin And fair needs foul," I cried. "My friends are gone, but that's a truth Nor grave nor bed denied."
William Butler Yeats