Jerzy Konorski (1903-1973) on the 20th anniversary of his death.

This article describes the pioneer research of Jerzy Konorski on voluntary motor conditioned reflexes type II (CRIIs or instrumental CRs). Some of his publications on topics such as four varieties of CRIIs, switching, and ability of transformation (plasticity) of CRIIs are briefly summarized. Konorski's theoretical views including criticism of some of Pavlov's interpretations are also presented. A few events connected to Konorski's scientific activities are mentioned.