“Where the only natural agents employed are those which are universally accessible, and therefore are practically unlimited in supply, the utility of the produce, or in other words, its power of producing gratification, or preventing pain, must be in proportion to the sacrifices made to produce it, unless the producer has misapplied his exertions: _Since_ no man would willingly employ a given amount of labor or abstinence in producing one commodity, if he could obtain more gratification by devoting them to the production of another.”[142] This passage, whether consciously or unconsciously, is a proposition about a primitive or a Robinson Crusoe economy. It affirms that the utility of products will be _in proportion to_ their total disutility costs of production, but it does not affirm that production will be carried on until the utility per unit of the increasing number of products will be reduced until it is _equal to_ the disutility cost of a unit. Except for the failure to make this latter observation, Senior’s formula looks like an anticipation of later theories of value. This appearance is carried out by the use of the word “utility” for value. The word as here used was probably taken directly from Say; it cannot be Adam Smith’s “_value in use_.” For if Crusoe produced at equal cost, measured in disutility, a small article of luxury and a great quantity of necessaries, and estimated the two at the same value—and this would be normal—the Smithian values in use distinctly would not be in proportion to sacrifice costs. The great quantity of necessaries would have a great “_value in use_,” as contrasted with the small article of luxury, for which Crusoe nevertheless was willing to expend quite as much labor. “Marginal” or “final” utility would fit the requirements of this formula, but there is nowhere in the book the slightest evidence that Senior utilizes the marginal method. In fact, on the same page with this proposition is a paragraph which shows that he considers the value of things not capable of increase in supply—the “rare productions of nature and art”—to be subject to no general rule, because dependent merely on the wealth and taste of the community.[143] That is to say, unless there is some ascertainable rule governing the conditions of the supply of goods, there is no rule of their value. But the utility theory is a whole explanation of value lying precisely in this region of no rules.[144]