Antithesis (Greek for "setting opposite", from ἀντί "against" and θέσις "position") is used in writing or speech either as a proposition that contrasts with or reverses some previously mentioned proposition, or when two opposites are introduced together for contrasting effect.
Antithesis can be defined as "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".
An antithesis must always contain double meanings due to the reproduction of two ideas within one statement. The ideas may not be structurally opposite, but they serve to be functionally opposite when comparing two ideas for emphasis.
According to Aristotle, the use of an antithesis makes the audience better understand the point one is trying to make through their argument. Further explained, the comparison of two situations or ideas makes choosing the correct one simpler. Aristotle states that antithesis in rhetoric is similar to syllogism due to the presentation of two conclusions within a statement.
The term antithesis when used in speech is sometimes confused with the use of irony, or "words [used] to convey a meaning opposite to their literal sense". The two are often mistaken for one another due to their creation of an opposite situation for the audience. The antithesis deals with two parallel ideas, whereas in irony, when used as a literary device, the words are implying an opposite idea directly through tone or word choice.
To make the meaning more clear, consider this example of irony: I cut my hand on a Bandaid box. The example is not an antithesis because it does not present two parallel ideas, instead it gives an implication of the opposite idea through its tone.
A simple counting of the elements of dialectics (any formal system of reasoning that arrives at the truth by the exchange of logical arguments) is that of thesis, antithesis, synthesis. Hell is the antithesis of Heaven; disorder is the antithesis of order. It is the juxtaposition of contrasting ideas, usually in a balanced way. In rhetoric, it is a figure of speech involving the bringing out of a contrast in the ideas by an obvious contrast in the words, clauses, or sentences, within a parallel grammatical structure, as in the following: