At first thought it may seem strange that value in use and value in exchange are the same thing looked at from two different points of view. We are accustomed to think of value in use as varying with the individual estimates of various persons and value in exchange as something which is the same for all persons at a given time and in a given place. The explanation is very simple. If individuals did not exchange goods and if each produced all of the things that he needed, each good would have a different value in use for every individual. Whenever a good becomes of comparatively little importance to an individual as compared with other goods, and with the estimate which other persons make of this good, a portion of it will be exchanged for some of the other good which has the relatively higher value in use. After a man has parted with a portion of his supply of the first good each unit of the remainder of that good has for him a greater value in use than before the exchange was made, owing to its greater scarcity. But after the exchange each unit of the second good has for him a smaller value in use than before, because of the greater quantity of it in his possession. He has increased the marginal utility of the first good and diminished the marginal utility of the second good. He will continue this process of increasing the marginal utility to him of one good and diminishing that of the other by decreasing his supply of the one and increasing his supply of the other until the marginal utilities reach a state of equilibrium, that is, until the utility to him of the amount of the first good which can be purchased for a given sum of money is equivalent to the utility to him of the amount of the second good which can be purchased for the same sum of money. When this condition of balance is reached a dollar's worth of the first good has for him the same value in use as a dollar's worth of the second good. Thus, values in use tend to approximate values in exchange.