grain is to make whisky, so the value of a fourth bag of grain is the value of his whisky. Only if he loses four bags of grain will he start eating less; that is the most productive use of his grain. The last bag of grain is worth his life. In explaining the diamond-water paradox, marginalists explain that it is not the total usefulness of diamonds or water that determines price, but the usefulness of each unit of water or diamonds. It is true that the total utility of water to people is tremendous, because they need it to survive. However, since water is in such large supply in the world, the marginal utility of water is low. In other words, each additional unit of water that becomes available can be applied to less urgent uses as more urgent uses for water are satisfied. Therefore, any particular unit of water is worth less to people as the supply of water increases. On the other hand, diamonds are in much lower supply. They are of such low supply that the usefulness of one additional diamond is greater than the usefulness of one additional glass of water, which is in abundant supply. Thus, diamonds are worth more to people. Therefore, those who want diamonds are willing to pay a higher price for one diamond than for one glass of water, and sellers of diamonds ask a price for one diamond that is higher than for one glass of water. Conversely, a man dying of thirst in a desert would have greater marginal use for water than for diamonds so would pay more for water, perhaps up to the point at which he was no longer dying. See also Paradox of hedonism References Paradoxes in utility theory Theory of value (economics) Paradoxes in economics