It is argued that both stimulus-response (S-R) and cognitive theories of learning and behaviour capture part of the truth, in that these terms involve two different types of process that are jointly responsible for the control of behaviour. The proposal that both processes coexist is investigated in the context of the production of behaviour. Evidence is presented to show that the weighting attached to S-R and cognitive processes can change as a function of (a) development; (b) experience; and (c) pathology. A model is proposed which is designed to sketch some ideas on how S-R and cognitive processes jointly determine behaviour, and it is related to the notion of behavioural hierarchy. It is argued that the model can help to develop a synthesis between psychology, ethology and neuroscience.