ABSTRACT
The case of Clever Hans is one of the most notorious episodes in the history of animal psychology. Among numerous “clever animals” of the time, this horse’s apparently human-like displays of mathematical, linguistic and musical understanding caused a stir in Germany just after the turn of the century. The “Clever Hans effect” has become the name of a cardinal scientific sin, the experimenter effect by which researchers inadvertently give their subjects the answers to their questions. Hans’s confrontation with the tests “without knowledge” proposed by the investigator Oskar Pfungst was decisive. Hans’s silence or stray responses to the blind questions marked him as guilty of having tricked the humans. Pfungst’s research takes place at a critical moment of the bifurcation of psychology: the transformations of Hans herald the transformation of subjects. Hans would have relied on someone else in the gathering who knew the number to generate, since he had heard it pronounced by Mr Schillings.
