If it be correct that pain cost and potentiality cost are the two elementary kinds of cost, what is the relation of the two historical forms of cost, labor and entrepreneur’s cost, to these? Just as the word labor stands for two distinct things, toil and productive power, so may “labor cost” mean either pain cost or potentiality cost. If the term labor cost is used without a qualifying adjective or explanatory phrase, it would naturally call up in most minds the conception of pain cost. But labor force is the most disposable of all productive agencies, and when the productive power of labor (what the entrepreneur buys) is used up in the production of a given commodity, we have a perfect example of potentiality cost. As we have seen, Adam Smith used labor at different times, both in the sense of toil or disutility and in the sense of productive power or potential commodity. Ricardo, to the best of the writer’s knowledge, said nothing to indicate definitively which of these concepts he designated by the term labor. In the writer’s judgment the presumption is that by the labor cost which regulates the exchange value of commodities, Ricardo meant what we call pain cost. At one place, Ricardo said “difficulty of attainment” is the true measure of value. It seems almost assured that this must mean “pain cost.” When cost is conceived as the ultimate essence of value, the cost will almost certainly be pain cost or “real cost.” It is interesting to note that Professor Dietzel, in arguing that the Ricardian labor theory of value is perfectly reconcilable with all that holds good in the utility theory, states that labor cost must be conceived solely as “_Nutzeneinbusse_,” _i. e._, utility-sacrifice, or potentiality cost. When the labor theory is founded upon the conception of labor as toil (“Unlust”), he considers it to be “built upon sand.”[207]