There are three reasons why we use sarcasm: 1) to criticize, 2) to save face, and 3) to be humorous.
It really doesn’t make sense to use sarcasm when you think about it. You are saying something you don’t believe—and you want people to know you don’t believe it so you roll your eyes or smirk or use a sneering or a snide tone of voice. Why not just say what you think? There are three main reasons why we use sarcasm: 1) to criticize or evaluate, 2) to save face, and 3) to be humorous. Let’s look at these reasons.
First, most people who use sarcasm are doing so to criticize or offer some judgment. There is a good chance that direct criticism or evaluation would place the speaker in jeopardy. For example, an employee criticizes an employer by saying he’s “such a great boss!” in a way that listeners realize is spoken sarcastically. The employee cannot directly offer criticism of the employer at work for fear that such criticism might get back to the employer. The same situation occurs with children (particularly teenagers who are old enough to understand the functioning of sarcasm) who wish to object to their parents’ demands and might say sarcastically, “Of course, Dad, I’d just love to mow the lawn!” They will probably get punished for their attitude, but their actual language is very positive and agreeable.
Second, and following from the first reason, is saving face. Most people use sarcasm because they are in a position where they cannot speak directly—at least not without adverse consequences. Take the employee in the example above. If he says, “The boss is a jerk” and this comment gets back to the employer, he is in trouble. With sarcasm, he has deniability. He can always point out that he said only positive things about the employer, which is true . Sarcasm is a much safer road and it allows him to save face with his employer. In the second example, the child, who we assume doesn’t want to mow the lawn, also saves face, and can justifiably argue that he does want to mow the lawn—after all, that’s what he said.
Third, in less serious situations, sarcasm is used by many people to be humorous and to show how clever they are. However, these humorous uses of sarcasm have no doubt evolved from the more serious forms, where sarcasm was originally used to criticize in a way that could covered the speaker’s true intentions and thus, allowed the speaker to save face. Sarcastic speakers who did so effectively were seen as clever and effective language users, and the ability to skewer someone with a sarcastic zinger is still important today.
Of course, not all humorous sarcasm involves criticism of others. Sarcastic speakers often present their funny remarks to critique situations, events, and even themselves. If you are intrigued by sarcasm, please check out my book "Sarcasm and Other Mixed Messages: The Ambiguous Ways People Use Language," published by Edwin Mellen Press, 2006.