Dichotomy means a division into two opposing parts. In literature, the author often uses dichotomy to create conflict. Some common examples of dichotomy in literature include good/evil, soul/body, heaven/hell, real/imagined, love/hate. Sometimes the dichotomy appears centered in one character, but often the author will use separate characters to represent the opposing sides.
Here are some examples:
From Star Wars, Luke Skywalker/Darth Vader-- Both representing the dichotomy between the Jedi and the Dark Side.
Dr. Jekyll/Mr. Hyde-- Here the dichotomy is centered in one character, representing good and evil.
The Hunger Games, The setting forms a dichotomy--the corrupt Capitol versus the honest, hard-working districts.
Without even understanding dichotomy, writers use it consistently in works where a sharp contrast is required. This is because dichotomy is a useful literary device which creates drama, causes conflict and adds depth to characters and situations. To simplify it it is useful to consider the conflict, for example, between good and evil, a popular literary theme.
Shakespeare uses dichotomy in his complex characters. Macbeth is a good example of the conflict between good and evil as Macbeth, rewarded for valor on the battlefield and considered the king's loyal ally, cannot fight his "vaulting" ambition which, he admits, "o'er leaps itself" and to which he refers in Act I, scene vii, line 27. Macbeth has the power to discount the witches' prophesies but, instead, due to his tragic flaw and his over-zealous wife, he transforms into a killing machine, callously attempting to dispose of anyone in his way.
Macbeth also contains the famous "foul and fair" analogy which first appears in line 10 of Act I, scene i. Despite the uncertainty that surrounds these words, as they forewarn the audience of what may follow, dichotomy is apparent in the struggle between the natural and the supernatural which would have attracted Shakespearean audiences who were both fascinated and terrified by it. There is a definite conflict between the Christian values of the audience and their superstitions and obsession with witchcraft. In Act II, scene iv, line 41, the audience is warned of those who "would make good of bad, and friends of foes."
Dichotomy is represented in Lord of The Flies by the democracy and order of the conch contrasted with the savagery of Jack and his hunters. Ralph and Jack reflect two opposing sides of the leadership struggle, despite the fact that they both have certain characteristics which could have, under different circumstances, complemented each other. By the end of the novel, however, the situation has changed and the dichotomy between good and evil is uncertain as the reader sees the change in Ralph who cries, "for the end of innocence."
Dichotomy is a division or contrast between two things that are truly different or are represented as being opposed or entirely different. Thereby, dichotomy illustrates a clear distinction between two objects. While metaphors and similes imply the similarities between two unlike objects through the use of comparison, dichotomy states outright the difference between two unlike objects or mutually exclusive events without the usage of comparison. Examples are sun and moon, fire and water, war and peace, the dreamer and the realist, etc.
Sometimes, the phrasing of sentences creates a false dichotomy. In a false dichotomy, the objects are not jointly exhaustive (there are other alternatives), or they are not mutually exclusive (the alternatives overlap). False dichotomy is created by logical fallacies and sentence phrasing such as in an "either/or" scenario. One such case is all insects either have six legs or eight, but a centipede is an insect and fits neither category.
A dichotomy is the division of a proposition into two parts which are both mutually exclusive - i.e. both cannot be simultaneously true - and jointly exhaustive - i.e. they cover the full range of possible outcomes. They are often contrasting and spoken of as "opposites". The term comes from dichotomos (divided): dich- ([in] two) temnein (to cut).
from Webster's Online Dictionary