To recur to our illustration. So long as the sailor had the two biscuits, one of them would go to satisfying the higher want (his own), and the other to satisfying the lower want (the dog’s), and either biscuit was capable of satisfying either want. But, when one biscuit was lost, the one that remained was instantly elevated to satisfying the higher want only: it rose, literally, in value because then it was not a man’s _or_ a dog’s life that depended upon it but a man’s only: what was lost was the means of satisfying the _dog’s_ want: the less important of the two wants was the dependent one; and it is the relation of dependence, as we said, that determines value. We may formulate the proposition thus. The value of a good is measured by the importance of that concrete want which is least urgent among the wants satisfied. And we find that what determines the value of a good is, not its greatest utility, nor its average utility, nor yet its least conceivable utility, but its marginal utility in the given circumstances. Jevons called this the Last or Final Utility. We shall follow Wieser literally in calling it the Marginal Utility. Simple as this proposition is, experience in teaching tells me that it is not easily retained so as to be used. For this reason, it may not be superfluous to confirm its truth by testing it in various circumstances. I cannot improve on Böhm-Bawerk’s admirable illustration, and only modify it in non-essential particulars. A modern Robinson Crusoe has just harvested five sacks of corn. These must be his principal maintenance till next autumn. He disposes of the sacks, according to the scale of his wants, in the following way. One sack he destines for his daily allowance of bread. Another he devotes to cakes, puddings, and the like. He cannot use more than these in eating, so he devotes a third to feeding poultry, and a fourth to the making of a coarse spirit. With these four sacks, we shall say, he is able to satisfy all the wants that occur to him as capable of being directly satisfied by corn, and, having no more pressing use for the fifth sack, he employs it in feeding dogs and cats and other domestic animals, the companions of his lonely life. The question is: What to him is the value of a sack of corn? As before, we ask: What utility will fail him if he lose one sack? It is inconceivable that Crusoe should have any doubt as to his answer: he will, of course, apportion out the sacks that remain as before;—two to food, one to poultry, one to spirits, and he will give up only the feeding of dogs and cats. This is seen to have been the Marginal Utility—the utility on the margin of economic employment or use. What he loses, then, by losing one sack is his former Marginal Utility; and this marginal utility undoubtedly determines the value of a single one of the five sacks. But here we come upon another feature of this valuation. If the marginal utility