Chapter Iv--Principles of Wages (_continued_) 69

§ 1. We have next to examine the causes of formation of relatively separate groups of wage earners.

§ 2. What is meant by a "relatively separate group"?

§ 3. The causes of the existence of these groups in the United States to-day. Inequality of natural ability; inequality of opportunity; artificial barriers. All these contradictory to assumptions behind theory of general rate of wages.

§ 4. Trade unions another factor in the formation of relatively separate groups. Indirect effects in opposite direction.

§ 5. Each of these groups has a relatively independent economic career. There are a series of wage levels, all of which are governed to a considerable extent by the same forces.

§ 6. The way in which the relative plenty or scarcity of each kind or group of labor affects its wages. Other forces play a part also.

§ 7. The nature of wage "differentials."