2 An important condition. The modification of conclusion necessary on taking account of changes in wants will receive careful attention in the next chapter.
especially after the addition of any more intense want, there will be a renewed effort to satisfy the whole range of wants even more completely than before. The margin falls in exact correspond ence with the success of that effort. The margin of consumption is therefore fixed by the relation between man and his environment.
The law of progress, so far as it affects the consumption of the individual, is that the mar ginal increment of consumption satisfies at each period a want of greater intensity than at the preceding period. There are two opposite ten dencies : one toward the improvement of the mechanical processes of production springing from industrial progress ; and one toward the development of new wants springing from social progress. The latter tendency deter mines the extent to which positive utility will be found to reside in commodities which had before been regarded as neutral or negative, and the extent to which the positive utilities of other commodities will be increased relatively to their cost. In a progressive society this latter tendency will prevail over the other in determining the actual position of the margin of consumption. Although the margin might
fall because of the fact that with a given amount of energy given wants are more fully satisfied, it is prevented from doing so by the growth of new wants and by changes in the relative intensity of wants that had previously existed. Commodities that had been entirely below the margin are brought above it by the discovery of new uses to which they may be applied. The work of the last hour of the laborer's day satisfies a want of greater inten sity than it previously did because of these changes in desires. If wants had not changed, that hour would satisfy a less intense want than it formerly did, because, each of the previous hours of the day having become more produc tive, all the more intense wants would have been already satisfied before that hour had been reached. Temporarily the margin may fall immediately after great changes in the pro ductive processes, but eventually, if there is social as well as industrial progress, the mar gin will rise, the law of progress being that the marginal increment satisfies continually a higher or more intense want.