Young Pierre has never left France, but he hears that London is an attractive city. He adopts the belief “Londres est jolie” (“London is pretty”).

Now Pierre’s family moves to another country, whose language he learns directly, without translation into French. He learns that his new city is called London, and eventually forms the belief that “London is not pretty.” He doesn’t know that Londres and “London” refer to the same city.

What are we to make of this? We can’t deny the sincerity of Pierre’s original belief, which he still holds; nor of his new belief; and it seems absurd to claim that he holds both or neither. “Each possibility seems to lead us to say something either plainly false or downright contradictory,” writes Princeton philosopher Saul Kripke. “Yet the possibilities appear to be logically exhaustive.”

“This, then, is the paradox. I have no firm belief as to how to solve it.”