Hawtrey points to a defect in the theory of an elastic supply of labour based on marginal utilities of product and effort, in "Trade and Credit" (1928). while a difference between the marginal utility of the product and the disutility of effort may prompt an additional supply of labour "in the simple case of a man working on his own account" (1928, p. 148), Hawtrey argues, this is not the general case since: "the decision as to the output to be undertaken is in the hands of a limited number of employers, and the workmen in the industry are passively employed by them for the customary hours at the prevailing rates of wages" (1928, p. 149). In this case output decisions are based not on the gross proceeds, but on the net profit margin.