4. The doctrine that, with the foregoing conditions understood, the exchange value of commodities is governed by the comparative quantity of labor required for their production, involves a number of questions with respect to the manner of determining _quantity of labor_. Ricardo did not carry his inquiry into these questions as far as modern critics of the labor theory have pressed theirs, but in the course of his writings he made three important observations on this subject. (1) In the first place, Ricardo distinguishes between _quantity_ and _value_ of labor. J. B. Say had in various places endeavored to state Ricardo’s position as being that the _value_ of labor determines the value of its products, for in this form the doctrine can easily be shown to involve a circle. Ricardo wrote to Say: “You misrepresent me ... when you say I consider the value of labour to determine the value of commodities; I hold, on the contrary, that it is not the value, but ‘the comparative quantity of labour necessary to production which regulates the relative value of the commodities produced.’”[53] The purport of this—though not so explained by Ricardo—is that the quantity of labor which an entrepreneur is compelled by the nature of a good to employ to produce that good, determines the amount of wages he has to pay for its production. As far as this single point goes, the answer to Say is satisfactory. (2) When Marx came to the question of skilled labor, he called it simply “condensed labor.” It goes without saying that he judged the degree of the condensation of any concrete skilled labor purely by its comparative wages, or exchange _value_.[54] Ricardo’s treatment of skilled labor is even less satisfactory than Marx’s. He says: “If a day’s labour of a working jeweller be more valuable than a day’s labour of a common labourer, it has long ago been adjusted, and placed in its proper position in the scale of value.”[55] What has long ago been adjusted? In definite words our author does not say, but his meaning is ascertainable. “If a piece of cloth be now of the value of two pieces of linen, and if, in ten years hence, the ordinary value of a piece of cloth should be four pieces of linen, we may safely conclude, that either more labour is required to make the cloth, or less to make the linen, or that both causes have operated.”[56]