A convenient point of departure for a consideration of the evidence in favour of cognition and imagery in animals is the controversy which existed in learning theory in the 1930s and 1940s. At that time the view had emerged and, in the interest of scientific respectability for the new psychology, had gained wide acceptance, that behaviour was best explained solely in terms of observable stimulus and response events (see Walker, 1983, chapter 3; Bolles, 1979, chapters 1–6). This view had developed from Thorndike’s earlier crusade to rid comparative psychology not only of the then popular anecdotal approach but of all appeals to ‘mental’ processes as explanations of observed behaviour. Instead he proposed an automatic process of ‘stamping in’ of reflexive associations between stimuli and responses, on the basis of the effects which the particular response produced. If the outcome had been ‘satisfying’ then the bond between the current stimulus complex and the successful response was strengthened, making that response more likely in the same situation on future occasions. This model of adaptive behavioural change effectively removed the need to suggest the existence in animals of processes akin to insight, reasoning or expectancy of outcome. The latter processes, Thorndike suggested, were the province of primate brains and human brains in particular. This mechanistic, reflexive view gained enormous credence from the 100independent work of Pavlov on classical conditioning, which was not only seductively objective in its methodology but lent itself to a description in reductionistic terms, relating stimuli and responses with no need for an appeal to intervening mentalistic events. This mechanistic approach was finally established as the mainstream of thought in psychology generally by the ‘behaviourism’ advocated by Watson (1925), and the stimulus-response (S-R) psychology of Hull (1943), which adopted an elaborate mathematico-deductive stance and was intended to encompass human behaviour as well as that of other animals.