Ideal types in sociology are most closely associated with the name of Max Weber, although as a method of investigation and explanation they are more commonly found in economics, for example in the concept of the perfect market. For Weber, the construction of an ideal type was clearly a heuristic device, or method of investigation. An ideal type is neither an average type nor a simple description of the most commonly found features of real-world phenomena. Thus one does not construct an ideal type of bureaucracy by finding the features that are shared by real bureaucracies. Nor is ideal used normatively in the sense of a desirable objective.
Ideal types are worked out with reference to the real world, but involve a selection of those elements that are most rational or which fit together in the most rational way. Thus the ideal type of bureaucracy embraces those aspects of real bureaucratic organizations that fit together in a coherent means-end chain.
Implicit in Weber's work is the view that constructing an ideal type is a way of learning about the real world. This is situated within a rationalist view of the human sciences: namely, that we all share a rational faculty, and the fact that we can think and act rationally gives order to the world. Thus, by constructing a rational ideal type, we learn something of how the world works. We can then learn more, by comparing the ideal type with reality, looking at how and why the real bureaucracy might differ from the ideal type. We do not end with a model of what a bureaucracy is, or of what it should be, but of what it might be if it were entirely rational. In this way we can learn much from the sources of apparent irrationalities in real bureaucracies.
The method is a difficult one and owes much to the neo-Kantian philosophical tradition from which Weber came. Anglo-Saxon sociologists have had trouble with it, and often treat ideal types as a sort of hypothetical model which can be tested against reality, thus giving Weber's account (at least) a distinctly positivist gloss. The best account will be found in Susan J. Hekman, Weber, The Ideal Type, and Contemporary Social Theory (1983). See also images of society.