THOG problem

The THOG problem is one of cognitive psychologist Peter Wason's logic puzzles, constructed to show some of the weaknesses in human thinking.

You are shown four symbols and told by the experimenter "I have picked one colour (black or white) and one shape (square or circle).

A symbol that possesses exactly one, but not both, of the properties I have picked, is called a THOG.

Presented in this form, the task is quite difficult, because much information must be held in working memory at the same time.

From the table we see that the only valid choice for the experimenter are the white square or the black circle.