The argument in the previous chapter points to the conclusion that, in order to reach an understanding of the industrial structure and behaviour that promote economy, efficiency and progress (and also of the criteria that should govern policy towards monopoly), we need a definition of competition more useful than that provided by welfare theory. Such a definition was offered by Professor J. M. Clark in his paper on ‘Workable Competition'.1 The theory of workable competition is concerned with the factors that stimu late economic rivalry and is, therefore, a dynamic concept. It tries to judge forms of industrial organization and the policies of firms by reference to the extent to which they promote or hamper this rivalry. It recognizes that monopoly elements are inevitably present in most market situations in modern industry and it seeks the ways in which these can be made compatible with active com petitive behaviour. The main condition for the existence of work able competition is that both buyers and sellers should have before them ‘an adequate number of alternative courses of action'. This concept is far from precise, and leaves the determination of what is ‘adequate’ to be decided in particular cases. Further, one must recognize that the existence of opportunities for competition does not ensure that they will be seized. This depends on the presence of a desire for active behaviour, or of an aggressive spirit, some where in the industry.