Among other things, rationality is the ability to make distinctions, to tell one thing from another, to know that x is not y. But, if rationality is categorical, sometimes it feels as though categories may be a category error. Faced by the perfectly rational idea that one knows the difference between “successful” and “unsuccessful” enterprises, Anton Chekhov once wrote to a friend: “Are you successful or aren’t you? What about me? What about Napoleon? One would need to be a god to distinguish successful from unsuccessful people without making mistakes. I’m going to a dance.” One feels that it wasn’t a mistake to go to that dance—not least because dancing isn’t entirely rational. On Sign o’ the Times, Prince ends that ridiculously danceable track, “It’s Gonna Be a Beautiful Night”, with the words “Everybody, groove,” pauses a second, and then closes by elongating one word more: “Confuuuuuuuuuusion.” To groove is to get confused, to know that knowledge isn’t all it’s cracked up to be, to...