The 'Strong' theory of advertising receives widespread support and is characterized by the beliefs that advertising increases peoples' knowledge, changes peoples'attitudes and, as a result, is capable of persuading people who have not previously bought a particular brand to start buying it and to persuade others who already buy it to do so with greater frequency and in preference to other brands on offer. Advertising is seen as being capable of increasing sales not only of brands but also of complete product categories and is a prime mover in the capitalist system. There is another theory, the 'Weak' theory, developed especially in Europe and strongly rooted in empiricism. Derived from Andrew Ehrenberg's Awareness-Trial-Reinforcement hypothesis, the 'Weak' theory argues that advertising is capable of increasing peoples' knowledge but actually communicates not very much: advertising is not strong enough to convert people whose beliefs are different from those championed in an advertisement: most advertising is employed defensively: members of the public frequently claim that they are not influenced by advertising and they are probably right. In general, according to the 'Weak' theory, consumers are apathetic and rather intelligent. The two theories are at opposite ends of the spectrum. It is easy to produce a great deal of circumstantial evidence to demonstrate that the Strong theory of advertising does not accord with reality. Research can make a major contribution towards providing the evidence which will help us all to better understand how advertising really works.