As a rhetorical scheme in literature, the positioning of contradictory ideas together creates antithetical concepts. For example, Dr. Martin Luther King's famous line, "We must learn to live together as brothers or perish together as fools," represents antithesis since it indicates the choice of these two extremes. The concepts don’t need to be total opposites but instead may indicate differences in their extent, such as with Neil Armstrong's, "One small step for man, one giant leap for mankind." Writers use antithesis to clarify their ideas and give the readers greater understanding of the concept.
When developing a written or oral argument, thinking about antithetical ideas or reasons the opposition would disagree, allows you to determine how contentious your topic is and to develop a more effective thesis and craft a strong refutation. Recognizing the opposition's ideas and refuting them with antithetical argument -- explaining why they are wrong or ineffective -- makes your argument more forceful. For instance, if you argue that tobacco products need a higher tax, you might bring up that opponent's statement that such a tax is unfair and then refute that idea by pointing out that the money helps offset medical issues associated with its use.