In truth, however, practically none of the assumptions underlying the theory of a general rate of wages are perfectly realized in the United States to-day, and some of them stand in almost direct opposition to the fact. It has come about, therefore, that different kinds of labor have relatively independent economic fortunes. The forces which govern distribution do not effect them equally. Facts and circumstances which enter into the determination of the level of earnings of one kind of labor may not affect the level of earnings in other groups. The differences between the level of earnings of the various groups cannot be explained entirely as "equalizing differences." The "perfect liberty" of choice of Adam Smith does not exist. Therefore, an investigation of wage principles requires study of two sets of forces and relationships. Firstly, of the forces which govern the outcome of distribution as between each and all of the labor groups and the other agents of production.[29] And secondly, of the causes of the formation of relatively separate groups of wage earners, and of the forces which govern the differences of wages between them. The first set of these distributive relationships has been the principal subject of this chapter. The other set will be the principal subject of the following chapter. Any policy of wage settlement must be based upon a knowledge of both sets. FOOTNOTES: [12] H. Clay, "Economics for the General Reader" (English edition), page 333. [13] See A. C. Pigou, "Wealth and Welfare," page 20. [14] A. Marshall, "Principles of Economics" (7th edition), page 138. [15] See pages 56-8, this chapter. [16] Address of Mr. Harrington Emerson at the National Conference of the "Society of Industrial Engineers and Western Efficiency Society" on labor problems. [17] G. D. H. Cole, "The Payment of Wages," page 67. [18] Final Report of the Committee on Industrial Relations (1912-16). Report signed by Commissioners Manly, Walsh, Lennon, O'Connell, and Garrettson--the section on scientific management stated to be based on an investigation conducted by Frey, Valentine, and Hoxie, page 128, Vol. I. [19] _Ibid._, Vol. I, pages 131-2. [20] R. F. Hoxie, "Trade Unionism in the United States," page 162. [21] London _Times_, Feb. 7, 1920. [22] G. D. H. Cole, "Payment of Wages," page 30. Discussion of the speeding up question. The best analysis of the problem created by the introduction of new and simplifying machine processes in skilled trades is to be found in a volume called "Labor, Finance, and the War," Report of the Committee of Investigation (1917), The Econ. Section, British Assn. Advancement of Science. In the same volume there is a careful analysis of the whole question of limitation of output. See also the chapter called "Unemployment" in Lord Askwith's "Industrial Problems and Disputes." [23] See A. L. Bowley, "Distribution of Income in the United Kingdom Before the War."