additional transaction equals the cost of making that transaction in the market. (At the lower limit, the firm's costs exceed the market's costs, and it does not come into existence.) In practice, diminishing returns to management contribute most to raising the costs of organising a large firm, particularly in large firms with many different plants and differing internal transactions (such as a conglomerate), or if the relevant prices change frequently. Coase concludes by saying that the size of the firm is dependent on the costs of using the price mechanism, and on the costs of organisation of other entrepreneurs. These two factors together determine how many products a firm produces and how much of each. Reconsiderations of transaction cost theory According to Louis Putterman, most economists accept distinction between intra-firm and interfirm transaction but also that the two shade into each other; the extent of a firm is not simply defined by its capital stock. George Barclay Richardson for example, notes that a rigid distinction fails because of the existence of intermediate forms between firm and market such as inter-firm co-operation. Klein (1983) asserts that “Economists now recognise that such a sharp distinction does not exist and that it is useful to consider also transactions occurring within the firm as representing market (contractual) relationships.” The costs involved in such transactions that are within a firm or even between the firms are the transaction costs. Ultimately, whether the firm constitutes a domain of bureaucratic direction that is shielded from market forces or simply “a legal fiction”, “a nexus for a set of contracting relationships among individuals” (as Jensen and Meckling put it) is “a function of the completeness of markets and the ability of market forces to penetrate intra-firm relationships”. Managerial and behavioural theories It was only in the 1960s that the neo-classical theory of the firm was seriously challenged by alternatives such as managerial and behavioral theories. Managerial theories of the firm, as developed by William Baumol (1959 and 1962), Robin Marris (1964) and Oliver E. Williamson (1966), suggest that managers would seek to maximise their own utility and consider the implications of this for firm behavior in contrast to the profit-maximising case. (Baumol suggested that managers’ interests are best served by maximising sales after achieving a minimum level of profit which satisfies shareholders.) More recently this has developed into ‘principal–agent’ analysis (e.g., Spence and Zeckhauser and Ross (1973) on