A paradox is an apparently self-contradictory statement, the underlying meaning of which is revealed only by careful scrutiny. The purpose of a paradox is to arrest attention and provoke fresh thought.
Paradox has a function in poetry, however, that goes beyond mere wit or attention-getting.
Modern critics view it as a device, integral to poetic language, encompassing the tensions of error and truth simultaneously, not necessarily by startling juxtapositions but by subtle and continuous qualifications of the ordinary meaning of words.