Bait-and-Switch Comparisons

By Geoffrey Pullum. I recently asked readers to think of a technical term for a kind of rhetorical structure for witticisms like the classic lawyer joke: “Q. What’s the difference between a catfish and a lawyer? A. One is a bottom-dwelling, scum-sucking scavenger, and the other is a fish.” It’s very familiar. But, I wondered, is there a suitably exact rhetorical technical term for the device?
I got some interesting suggestions in the Comments (24). Some felt far too general: Gavin Moodie suggested counterpoint; a commenter called chaucered came up with sleight of word; John Baker held that conundrum might do; but none of these seemed focused enough to me. More...