Note carefully that on the one diagram are represented a large number of marginal utilities which never exist at one and the same moment. At any one moment there is a given number of units and there is but one marginal utility, and this is the same for each of the units. It is quite erroneous to say that when there are 30 units the utility of the tenth unit is 36; of the twentieth, 25; of the thirtieth, 19. It is equally incorrect to say that when there are 60 units the "total utility" is equal to the area between the right angle and the curve a-g, while the value is equal to the rectangle below and to the left of the point g. The curve from a-g but marks the height of marginal utilities that have no existence when the supply is 30. The "total utility," often spoken of in this connection, if it has any existence certainly cannot be calculated. The diagram must be understood as representing indicatively at any given moment but one marginal utility, the same for every unit of like goods. The other perpendicular lines are expressed in the conditional mood; they are what the marginal utility would be were the numbers of units different. [Sidenote: Changing feelings changes utility] 5. _Since goods possess utility only as they gratify wants, it follows that if wants change, the utility changes._ Utility does not rest unchanging in the goods as something "intrinsic," but it depends on the relation of goods to men. This truth, unrecognized for many centuries, is now seen to be fundamental to the whole problem of value. The portions of a good added later do not appeal to the same man as the earlier portions. The man has been changed by what he has enjoyed. In changing his feelings, goods have also changed his wants. Hence, the added portions of the good are changed in respect to their utility or power to gratify a man's wants. Though physically and chemically, _i.e._, in every material way, they are exactly like the earlier portions, they cannot have the same want-gratifying power until he again changes, for they are not in the presence of the same feelings.