For much of the 20th century, mainstream american psychology tended to downplay inherent or biologically ingrained differences between people and emphasized instead the power of social environments in which we live. Behaviourism is a brand of psychology that explores the ways in which observable behaviour is learned and shaped by the environment. In the 18th and 19th century, the philosophy of utilitarianism put forth the idea that the good society should make for the greatest happiness or pleasure for the greatest number of people. The doctrine of associationism purports that various objects and ideas that are contiguous in time or space come to be connected, or associated, with each other into meaningful units. Classical conditioning represents one such form of simple learning. Classical conditioning can create something called stimulus generalization. In some cases, such complex associations are achieved through higher-order conditioning.