We all know that human behaviour is very complex; need complex theory to explain behaviour. Classical times: gods caused human to do things; gods are the complex mechanisms; something complex, powerful, and mysterious was needed to explain behaviour. Behaviourists argue that behaviour is caused by one"s life history of conditioning i. e. reinforcements; complexity is in the idea of one"s life-history; to know entire history in detail is impossible. Theories of behaviour answer a human need: to understand the system of the world; makes world seem less unpredictable. Cognition is about us; we begin with a need to find the system. No evidence integrated concept of mind existed. Reference to many functions, but not to relations among functions. Words for memory, perception, language, but not mind. Gods and demons were thought to interfere with human activities. Idea that behaviour comes from outside the person. Modern echoes of idea that behaviour comes from outside the person.