The economic order of consumption is modified by the mental act by which the increase of utility is imputed, i.e., attributed to the various ele ments which compose the group. The pleasure from a complement of commodities is a unit, but the complement itself is complex. Each of the commodities will be recognized to have con tributed at least that amount of utility which it would have had if consumed in isolation ; but after all the commodities have had that amount assigned them, there will remain all the in crease of utility which results from the forma tion of the complement. This increase is not, as might at first be expected, distributed evenly or in proportion to the original utility of the commodities. On the contrary, there is always a tendency to concentrate the whole of the increase on that one element or on the limited number of elements which have been last added to the complement, and which are there fore looked upon as having completed it, and thus added to the utility of all the other mem bers of the group. At a dinner, for instance, the agreeable result of the meal as a whole is apt to be attributed to some new or favorite dish, the absence of which, though the dish has of itself no great utility, would spoil the entire meal. In an academic course the student is always inclined to account for the benefit which he knows that he has received from the course, by referring to the instruction of a favorite teacher. At a concert the listener will attrib ute to some special performance the pleasure afforded by the entire programme. This act of imputation is a mental act. The principle, in accordance with which the utilities of certain commodities are increased, because of their relation to other commodities in the group of which they form a part, is a psychological principle. Commodities are desired in a differ ent order because the utility of certain com modities is thus increased. The economic order of consumption is modified, therefore, by the imputation of utility.
The final increments of the different commodi ties consumed tend to rise and fall together. Attention has already been called to the fact that commodities are consumed in a certain order, and that the successive increments of each commodity satisfy wants of steadily dimin ishing intensity. By the final increment of any commodity is meant the last increment actually consumed. By the marginal increment of con sumption is meant the final increment of the last commodity added to the consumption. It might be supposed that this marginal increment would satisfy a much lower desire than the final increments of the commodities which have pre cedence in the economic order. If it were a question of the initial increments of each com modity instead of the final increments, there would be such a difference. But the final incre ment of this last commodity has as great, or nearly as great, utility as the final increments of any of the preceding commodities. The differ ences in the pleasure obtained from different commodities are to be found, not in their final, but in their earlier increments. At the point where the consumption is broken off they have about equal power of conferring pleasure ; other wise the consumer would transfer a portion of his expenditure from the commodity which gave less pleasure, to one which gave more. In this way a more intense want for the first commod ity would be left as the final want, and a less intense want for the second commodity would be satisfied. For instance, food to the starving, shelter to the homeless, crowd out all other thoughts ; but, with a dollar to spare, a man may hesitate whether to indulge in a joint of beef, to have a broken window-pane set, or to buy Lorna Doone and read it to his family. It
might happen that radical changes in the desires of a consumer would leave.his consumption tem porarily in the condition indicated by the follow ing scale : The final increment of the larger number of commodities is 5. But there are three modities, say newspapers, woollen clothing, and rocking chairs (C, D, and K), of which the final increments remain 6, 7, and 6, respectively ; while two other commodities, say house accom modation and table silver (A and H), satisfy their respective wants so fully that their final in crements fall in utility to 4 and 2. This unbal anced condition cannot long remain. The more intelligent the consumption, the more quickly will normal conditions be restored. A slight reduction in house rent, and a considerable re trenchment in the expenditure for table silver will allow a daily newspaper to take the place of a weekly ; will allow a more adequate supply of woollen clothing, and the purchase of an addi tional rocking chair. This readjustment of con sumption to the conditions brought about by the growth in intensity of certain desires, as compared with others, is continually in progress. Its tendency is to cause the final increments of all commodities to satisfy wants of equal inten sity ; in other words, to cause the final incre ments of all commodities to have equal degrees of utility.
The margin of consumption is fixed by the re lation between man and his environment. From the preceding discussion it will be seen that the margin of consumption may be regarded as a straight line, or one continually tending to be come straight, and forming the boundary line of actual consumption. In the illustration above given, after readjustment is complete, the mar gin is a straight horizontal line passing below the final increments of the commodities. The margin may be indicated by the omission of the numbers below it, as in the preceding illustra tion, or by the drawing of a line, as in the fol lowing illustration : All commodities have a definite relation to this line, their successive increments ranging either partly above and partly below or entirely below it. Of commodities which begin with a very high degree of utility, a considerable number of increments will be found above the margin, i.e., a considerable quantity of the commodity is consumed ; of others but few increments are above the margin ; while still others, and always vastly the greater number of commodities, are, for the man of moderate means, entirely below the margin. They may be conceived as arranged in a particular way below the margin, waiting, as it were, until the margin falls far enough to include them, and certain to make their appearance at that time in accordance with a definite order, the eco nomic order of What is the rea son for the changes in the position of this line, for the rise or fall in the margin of consump tion ? The broadest answer is that it is fixed by the relation existing at the given time be tween man and his environment ; and for our present purposes this answer is sufficiently accurate. Man's power over nature is indi cated by his ability to utilize more efficiently the natural resources in the satisfaction of his desires. As this power increases, the margin of consumption falls. With each step in indus trial progress, wants of less and less intensity are satisfied. If we disregard changes in human a fall in the margin of consump tion will be regarded as an indication of prog ress. After each increase in the variety, and This .order is of course not fixed in the sense that it is in capable of modification. The object of this entire chapter is to show that it is continually changing, but in accordance with principles which may be investigated and clearly established.