Antithesis (from the Greek anti = against and thesis = position) is a figure of speech involving a seeming contradiction of ideas, words, clauses, or sentences within a balanced grammatical structure. Parallelism of expression serves to emphasize opposition of ideas. The familiar phrase “Man proposes, God disposes” is an example of antithesis, as is John Dryden's description in “The Hind and the Panther”: “Too black for heaven, and yet too white for hell.”
In grammatical usage antithesis is often expressed by means of an antonym, such as high - low, to shout - to whisper, lightness - heaviness, etc.
A simplistic description of dialectics is thesis, antithesis, synthesis.
See also: alternative hypothesis