The third canon of distribution, that of efforts and sacrifices, would be ideally just if we could ignore the questions of needs and productivity. But we cannot think it just to reward equally two men who have expended the same quantity of painful exertion, but who differ in their needs and in their capacities of self development. To do so would be to treat them unequally in the matter of welfare, which is the end and reason of all distribution. Consequently the principle of efforts and sacrifices must be modified by the principle of needs. Apparently it must also give way in some degree to the principle of comparative productivity. When two men of unequal powers make equal efforts, they turn out unequal amounts of product. Almost invariably the more productive man believes that he should receive a greater share of the product than the other. He believes that the rewards should be determined by productivity. It is evident that the rule of efforts and sacrifices, like those of equality and needs, could not be universally enforced in practice. With the exception of cases in which the worker is called upon regularly to make greater sacrifices owing to the disagreeable nature of the task, attempts to measure the amounts of effort and painful exertion put forth by the different agents of production would on the whole be little more than rough guesses. These would probably prove unsatisfactory to the majority. Moreover, the possessors of superior productive power would in most instances reject the principle of efforts and sacrifices as unfair, and refuse to do their best work under its operation. The three rules already considered are formally ethical, inasmuch as they are directly based upon the dignity and claims of personality. The two following are primarily physical and social; for they measure economic value rather than ethical worth. Nevertheless, they must have a large place in any system which includes the factor of competition. _The Canon of Productivity_