We have already established the principle that the possessor of a suit of clothing values that suit more highly than he would a second one exactly like it, and that a third would yield even less satisfaction than the second. Let us suppose, then, assuming that he has three suits exactly alike, that he attempts to determine the value to him of any one of the suits. We have seen that one suit was absolutely necessary, and that the other two were much less so. Certainly, then, being in possession of three suits, he will not say that any one of them is necessary, for he would still have two left if one were taken away. Obviously, therefore, the valuation he will place on any one of the three suits would be less than the valuation he would place on one suit if he possessed no other. Nor, by the same reasoning, will he value any two of the three suits as highly as he would if he had but two. He will, however, consider any one of the three suits as having exactly the same value to him as another suit would have if he already possessed two. We are now ready to state the law of marginal utility: The marginal utility of a series of goods is the utility of the last unit. This utility, we may say, is measured by the use to which the last unit can be put. If, to use an extreme example, he used the third suit to dress a manikin, then the value he would attribute to any one of the three suits would depend entirely on the satisfaction, slight as it might be, which he would derive from that particular use.