In view of the fact that the word _average_ as often serves to cover up the lack of an explanation as it serves to explain, Cairnes would have done well to be a little more explicit. As the present writer understands it, a few additional words will place his idea beyond possible misconception. If we call the capitalists who can furnish a given sum of capital at a small sacrifice, and the laborers who can furnish a given amount of labor (in the sense of productive power) at a small sacrifice, strong producers, and call others who are situated in reverse circumstances from these, weak producers, Cairnes’s proposition about “average sacrifice” means that “within a given field of competition” we may expect the individually strong and individually weak producers to be thoroughly and uniformly intermingled. With this meaning, the statement certainly commands assent. With this idea understood, we are able to speak of the labor of coal miners as being harder than that of dry-goods salesmen, without thought of the unusual cases where a very healthy miner suffers less fatigue and discomfort than an invalid salesman. 4. Proceeding with labor and abstinence as cost of production, Cairnes describes the relation of cost to value in terms clearer than any before attained in the regular line of English “_Principles_.” Wages and “profits” are derived from the value of the product, and “absorb the whole of that value,” “with the exception of the case where rent is also an element in the value of commodities—a case which, those acquainted with the economic theory of rent will perceive, does not affect the general argument.”[181] These words make the sum total of Cairnes’s discussion of rent, though he has written a large volume devoted chiefly to value and distribution. Value is then everywhere divided into wages and profits. If these wages and profits are in proportion to the sacrifices remunerated, value is in proportion to the sum of these sacrifices, or cost of production. The question, then, becomes definite. Are wages everywhere in proportion to the labor for which they are paid, and is interest an amount proportionate to the abstinence remunerated? Strange as it may seem, this simple question—the affirmative answer to which is necessary to establish the regulation of exchange value by “real” or subjective cost of production—was never proposed by Mill or any of his classical predecessors.