People use their means for the most important ends. If they have to give up a unit of their stock, they will continue to satisfy the more important ends. The satisfaction provided by the marginal unit is called marginal utility.
People make decisions on the margin. No one chooses between "guns" or "butter", but between a definite amount of guns and a definite amount of butter.
As an actor acquires more and more units of a good, he devotes them to successively less and less urgent ends (i.e. ends that are lower on his scale of values). Therefore the marginal utility of a good declines as its supply increases. This is the law of diminishing marginal utility.
- Murray N. Rothbard. "B. The Law of Marginal Utility", Man, Economy and State, online version, referenced 2009-07-07.
- Robert P. Murphy. "A Study Guide to Murray Rothbard's Man, Economy, and State, with Power and Market", Chapter 1, referenced 2009-07-07.