Professor Clark has in some place defined subjective value as the “measure of effective utility.” Menger defined this kind of value as the significance attained by a good in our estimation when we know that some satisfaction of ours is conditioned upon command of this particular good. Value, as an amount, is the measure of the quantity of satisfaction conditioned. The present writer has already expressed his opinion[240] that Menger’s mere definition of value gives the solution to the great riddle of the relation of value to usefulness and satisfaction, and that virtually from the mere proposition contained in this definition a large part of the theory of value can be deduced directly. It is of great interest to note, therefore, that Professor Clark’s definition of subjective value is in entire harmony with Menger’s. The definition of Menger explains value universally, wherever there is value. Clark’s definition, though conceived quite independently by him, is but an extension of the principle in Menger’s definition, but an application of it to a certain special case. This case, though logically a special instance, is however typical of most of the goods we imagine a Crusoe to be producing, consuming and reproducing. This is the case of freely reproducible goods. Here, if a good be destroyed, its value will be revealed by the satisfaction that must be given up because of its destruction, which is the satisfaction finally conditioned upon it. In the end, what Professor Clark points out is merely that this good may be replaced by diverting to its making labor which otherwise would have been employed in producing some other good which Crusoe chooses to resign instead. The satisfaction in effect, or in the end, conditioned by good A is the satisfaction directly conditioned by or afforded by good B, the good given up.[241] As it appears to the present writer, Clark’s theory of esteem value is to this point so well founded that even the most uncompromising opponent of labor theories can find no ground to deny it. We have here explained a labor measure of esteem value, perfectly justified at least under the conditions of the isolated economy, and Professor Clark’s analysis has disclosed the inner reasons why this measure can be employed. Indeed, while speaking of reproducible goods in the Crusoe economy, it may be affirmed that cost is not only a “measure” of esteem value, but is also a joint _regulator_ of value. To be precise, the costliness of a good acts jointly with the utility of the good in regulating its value. To say that one thing regulates another is, of course, asserting more than that it measures that other. A regulator is a measuring cause, whereas a mere measure is not a cause of the thing estimated.[242]