This paper analyses an interesting story, that of the physiologist Ivan Petrovitch Pavlov. While investigating the causes of salivary secretions in the waking, behaving dog, he discovered a class of causes that he called psychic, since they were associated with perceiving a visual, acoustic or other signal, delivered before food that normally created salivation. A temporary relationship was therefore established, between the secretory command and the cerebral site associated with an initially neutral stimulus that had become a signal. This gave rise to the "conditional reflex". Pavlov was probably not the first who had observed this kind of association, but he very skillfully exploited these data to create a coherent conceptual system. In 23 "lectures", he very precisely summarized his views and retraced the fundamental issues explaining the main features of the purely physiological cerebral command of behaviour. The Pavlovian system necessarily became, in the particular environment of the soviet regime, a kind of credo on physical-mental relationships based upon a generalized reflexology, not allowing any deviation, nor any dissidence, nor any concession to subjectivity. The notion of conditional reflex has indeed resisted to time, but number of subtleties of the Pavlovian thinking and many phenomena that he described now seem forgotten and to have lost much of their heuristic value. Most of the recent theories of learning have only rarely followed Pavlov's line, to concentrate on more complex learning modalities.
