While this conception of productivity is relatively simple, and the canon of justice based upon it is somewhat plausible, neither is adequate. To many situations the productivity test is substantially inapplicable. The removal from industry of the man who works alone; for example, the independent shoemaker, blacksmith, tailor, or farmer, would result not in a certain diminution, but in the entire non-appearance of the product; and the removal of the capital or tools would have precisely the same effect. According to the former method, the labourer is to be credited with the whole product, and capital with nothing; according to the latter method, capital produces everything, and labour nothing. Even when several labourers are employed in an establishment, the test is inapplicable to those who are engaged upon indispensable tasks; for example, the engineer in the boiler room of a small factory, and the bookkeeper in a small store. Remove them, and you have no product at all; hence a rigid enforcement of Professor Carver's test would award them the whole product. To be sure, we can get some measure of the productivity of these men by observing the effect on the product when inferior men are put in their places; but this merely enables us to tell how much more they are worth than other men, not their total worth. Moreover, even the substitution test is not always practicable. The attempt to ascertain the productivity of a workman of high technical skill by putting in his place an utterly unskilled labourer, would not yield very satisfactory results, either to the inquiry or to the industry. In the majority of such cases, the difference in the resulting product would probably far exceed the difference in the existing wage rates of the two men, thus showing that the skilled worker is getting considerably less than he is "economically worth."