Throughout the first half of the twentieth century, psychologists tended to believe that the explanations offered by classical and operant conditioning were fully adequate to understand human behaviour. Classical conditioning is a form of learning in which a conditioned and unconditioned stimulus become associated, such that the former comes to elicit a response previously elicited only by the latter. It is also known as the Pavlovian or respondent conditioning. Operant conditioning is a form of learning in which voluntary behaviour becomes more or less likely to be repeated depending on its consequences. It is also known as Skinnerian or instrumental conditioning. However, it is now believed that there are many other factors involved in human behaviour, such as cognitive factors, especially observational learning/modeling, and as most of these are based around experience, they are often grouped loosely together under the umbrella term of the social learning mechanisms. Dollard and Miller (1950) stated that, in humans, most learning is social and acquired through observing other people in social situations. Their Social Learning Theory, whilst having its roots in Skinnerian principles, aims to offer a more complex theory of learning in humans within a social context. Bandura (1977) states: "Learning would be extremely laborious, not to mention hazardous, if people had to rely solely on the effects of their own actions to inform them what to do." According to Bandura, the major theorist in the social learning theory, learning occurs in two ways: Response consequences and modeling/observational learning. Response learning is not dissimilar to the approach adopted by Skinner, in that the behaviors, which occur as a result of such learning can either, be reinforcing or punishing. Modeling or observational learning, Bandura et al. (1961) argued, is a form of secondary learning, by which we observe and model our behavior on those around us.