We use air quotes for many reasons. There’s the conspiratorial use, as when Mr. Trump questioned Mr. Obama’s legitimacy by referring to him as the “quote ‘president’ ” during his campaign. That, you might say, is old-fashioned, street-fighting politics.

There’s the self-subverting air quote, as when the Chicago White Sox manager Ozzie Guillen said, after using slurs against gays in 2006, “I will apologize to the people I ‘offended.’ ”

Then there are the times when air quotes backfire, seeming to reveal something otherwise hidden about the speaker’s meaning. Consider the criticisms of Senator John McCain who, while discussing abortion in 2008, air-quoted “health of the mother.”

In the 1990s, the “Saturday Night Live” comedian Chris Farley had a skit in which he made fun of all of this. “Maybe I’m not ‘the norm,’ ” he said. “I don’t ‘own a toothbrush’ or ‘let my scabs heal.’ ” It’s hilarious because he’s doing it wrong. But it also raises the question: If everything is air-quotable, then what does anything really mean?

We didn’t always have to contend with such ambiguity. People may have used air quotes as early as the 1920s, but they really came into vogue in the late 20th century. In a 1989 essay, “The Irony Epidemic,” Kurt Andersen and Paul Rudnick called air quotes “the quintessential contemporary gesture that says, ‘We’re not serious.’ ” Earnestness was out. Sarcasm was in. Nothing meant what it seemed to mean.