ABSTRACT
Piaget worked out his logical theory of cognitive development, Köhler the Gestalt laws of perception, Pavlov the principles of classical conditioning, Skinner those of operant conditioning, and Bartlett his theory of remembering and schemata—all without rejecting null hypotheses. But, by the time I took my first course in psychology at the University of Munich in 1969, null hypothesis tests were presented as the indispensable tool, as the sine qua non of scientific research. Post-World War 2 German psychology mimicked a revolution of research practice that had occurred between 1940 and 1955 in American psychology.
