What is foolishness (sottise, Torheit, stultitia)? Foolishness and stupidity are by no means the same thing. Stupidity is opposed to intelligence. Someone who cannot calculate in his head, who stumbles in her native language, or cannot spot an opportunity, or….—the list is very long—is sometimes said to be stupid or, slightly less stupidly, to be more stupid than some mean. Perhaps intelligence is what intelligence tests measure. Perhaps it is the ability to grasp a variety of internal relations without experiments. Whatever stupidity is, it is no vice, unlike foolishness. In order to see what the vice consists in, let us consider some traditional examples of foolishness.