William J. McGuire
People communicate for many reasons. They communicate in order to give information, to ask help, to give orders, to make promises, to provide amusement, to express their ideas (or, as Voltaire said, to hide them). The present discussion deals with another important function, persuasion. Much of the communicating that people do is intended to persuade someone to change his attitudes or the way he behaves. Because persuasion is both a very common and a very important reason for communicating, it has received a great deal of attention from psychologists interested in social interaction.
The study of persuasion is interesting both on scientific and on practical grounds. On the scientific side, it helps us to understand better why people behave the way they do, and why their behavior sometimes changes. On the practical side, an understanding of persuasive techniques would have obvious value to an advertiser, a politician, an educator-to anyone whose job it is to change what people think and do. It is probably not surprising, therefore, that the amount of research devoted each year to this topic has been growing even faster than the burgeoning rate of psychology as a whole. There have been literally hundreds of experiments on persuasive communication during each of the past decades.
As soon as we begin to think seriously about the process of persuasion, it is obvious that an enormous range of factors can contribute to its success or failure. In order to study persuasion analytically, we would like to vary each of these factors and see what effects they have. Each of these variable factors -- or