Examples of oxymorons include the phrases "jumbo shrimp," "Great Depression," "act naturally," "plastic glasses" and "deafening silence." The word oxymoron is itself an oxymoron, as it combines two Greek words with contradictory meanings. "Oxy" means sharp while "moron" or "moros" means dull.
A writer can use an oxymoron to add drama, to describe something in a new way or for humor. While short phrases are commonly used for oxymorons, authors also use entire sentences to create them. An oxymoron can add drama because it showcases two qualities of the subject. For example, the phrase "deafening silence" tells the reader that the silence is so intense that it has a deafening effect.
Since contradictory words aren't typically used together, an oxymoron can provide a unique way of describing a subject. The Great Depression was a difficult time for the United States, and adding the word "great" sets this depression apart from past and future economic downturns. When used for humorous purposes, the author uses an oxymoron to show off his wittiness for the audience. Oscar Wilde does this when he writes that he is able to resist anything except temptations.
While oxymorons are used often in literature, they are also a part of normal English. Since oxymorons are used frequently, readers typically don't notice them unless they make an effort to find them.