The Simple Logical Puzzle That Shows How Illogical People Are

In the 1960s, the English psychologist Peter Wason devised an experiment that would revolutionize his field. This clever puzzle, known as the “Wason selection task,” is often claimed to be “the single most investigated experimental paradigm in the psychology of reasoning,” in the words of one textbook author.

Wason was a funny and clever man and an idiosyncratic thinker. His great insight was to treat reasoning as an enigma, something to scrutinize both critically and playfully. He told his colleagues, for instance, that he would familiarize himself with their work only after doing his own experiments, so as not to bias his own mind. He also said that before running experiments, researchers—quixotically—should never really know exactly why they were doing them. “The purpose of his experiments was not usually to test a hypothesis or theory, but rather to explore the nature of thinking,” a pair of his students wrote in Wason’s obituary. (He died in 2003.) “His aim was to reveal a surprising phenomenon—to show that thinking was not what psychologists including himself had taken it to be.”

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