 Some authors have argued that preference change is only a superficial perception, and that the underlying preferences remain stable over time. But there are at least four arguments to the effect that people’s preferences really do change over time. First, many successful explanations of behavioural change have interpreted the empirical behavioural evidence as preference change. These explanations can be differentiated into models of external influences and models of internal coherence. External influence models attempt to establish general links between external events and agents’ preference formations. They include, for example, social imitation (Leibenstein 1950), parental influence (Cavalli-Sforza 1973), habit formation (Pollack 1976), and the effect of production patterns on consumption (Duesenberry 1949). Internal coherence models take certain external influences as given, and model preference change as an accommodation of these external influences. They include, for example, religious convictions (Iannaccone 1990) and the effect of cognitive dissonance on preferences (Elster 1982).