The economist ordinarily draws a series of supply curves designed to show the relationship between cost per unit and units produced on the assumption of static conditions and usually without regard to the frequency distribution of units produced in relation to cost per unit. Accordingly, he focuses his attention on definitions of the marginal unit, of the marginal cost per unit, and of the marginal producer. This is largely because he wants to equalize price and marginal cost to obtain a rational theory of value under his own premises. It is true that the economist will not ignore variations about the margin and will even concede that, under dynamic conditions, you may arrange producers in series from low cost to high cost and that for the time being differential entrepreneurial costs will become manifest. It is assumed, however, that these variations will tend to disappear the closer dynamic conditions settle down to static or equilibrium conditions. But the variations do not disappear and we would be extremely surprised if they did; indeed, the probability of uniformity of unit costs of production for any given number of producers is mathematically remote. The important thing, however, is the degree of variation that actually occurs under certain conditions or for a certain number of producers or for a certain industry. If we approach the problem in this way we may bring reality to economic analysis, improve the working tools of marginalism or correct its inadequate theoretical structure.