(taken from wiseGEEK)
In literature, post-irony generally refers to a return to sincerity when the author or character was previously speaking ironically or sarcastically. Some kinds of post-irony literally refer to a change of heart on the part of an author or character. Other kinds of post-irony refer to previously written works that were ironic in their time but are no longer considered as such. A third version of this literary device refers to a moment in which a character or author is being both ironic and sincere at the same time. This last use of this device is often done accidentally, as it is often difficult to combine sarcasm and sincerity on purpose without sounding contrived.
The first definition for post-irony, wherein a character switches between sarcasm and sincerity in the blink of an eye, can be seen in many works of literature. In Shakespeare’s play Hamlet, for example, the title character sometimes becomes the pillar of post-irony. After the appearance of his ghostly father, Hamlet’s speeches constantly wash between ironic ramblings and very sincere and earnest truths. This happens most often when he is speaking to his Uncle Claudius or his mother, Gertrude. He answers their questions with sarcastic, often unhinged, statements and then emphasizes them with earnest and sinister asides to the audience.
The second definition for post-irony, when something previously ironic is no longer perceived that way, can be seen in older works of literature and film. In the film The Graduate, for example, the main character, Ben, is approached by one of his father’s friends. This older gentleman advises Ben to get involved in the production of plastics. In 1967, when the film was made, this scene was viewed as ironic. Plastics were not necessarily seen as a forward-thinking thing in which to invest and the result was uproarious laughter from the audience. Modern viewers of this film often see this scene as good advice since plastic production later became a large and lucrative business.
The third version of post-irony, where it becomes jumbled with sincerity, is possibly the hardest type to pinpoint. One example of this kind of post-irony may be evident in Jonathan Swift’s satireA Modest Proposal. This essay states that if the Irish under English rule don’t have enough resources to feed their children, they should eat them. Swift says that this would solve the overpopulation problems, and that the Irish would have an unlimited supply of food. Of course, this was an ironic essay because Swift did not intend for Irish families to turn to cannibalism. He did intend to attract attention to a very serious problem however — Irish families were starving and the English were doing nothing about it. This work of literature carefully conflates sarcasm and sincerity so that the reader may see both sides of the issue at hand.