Say a name out loud. Cicero. Feynman. Your grandmother. Something has just happened that nobody can fully explain: a noise made in a room has reached out and fastened onto one specific thing in the universe, and it has done so even if almost everything you believe about that thing is wrong.

Saul Kripke spent his career on the question of how that trick works, and his answer took the ground out from under two generations of philosophers. Names, he argued, are not shorthand for descriptions. They are anchors. They hold onto the same object across every way the world might have turned out, which is why a fact discovered in a laboratory can turn out to have been unavoidable all along, and why some things you can know without checking might easily have been false.

This book follows those arguments and the extraordinary mind that produced them. We watch a graduate student who was not yet a graduate student invent the standard picture of possibility and necessity. We meet the imaginary Mr. Schmidt, who proved the incompleteness of arithmetic and got no credit for it. We follow a monolingual Frenchman named Pierre into a London he does not recognize as the city he has admired all his life, and out the other side of a puzzle about belief that has no accepted solution to this day. We watch pain and the firing of nerves come apart in a way that embarrassed the confident materialism of the age. We sit with a liar sentence until it stops moving. And we spend a chapter with the rule-following paradox that ate the philosophy of the 1980s, which everyone now calls Kripkenstein because it belongs entirely to neither of the men in the name.

There is also a human story here, and it is stranger than the usual academic biography. A boy in Nebraska with an intellect that alarmed his teachers. A young man whose only earned degree was a bachelor's, and who never saw the point of getting another.