[Sidenote: Concrete conditions of industry must be studied with wages] 1. _The law of wages must be considered in connection with other far-reaching influences._ One may use the sentence, "the marginal productivity of labor determines wages," without having a true understanding of its meaning. Memorizing a definition is only the first step toward economic reasoning. Till that definition becomes a real thing in the student's thought it helps him but little. The law of wages is an abstract statement of the logical relation of wages to utility; it is not a concrete statement of the industrial conditions in which labor works, yet these are more nearly in the nature of true causes of value. The marginal utility is itself determined by forces and conditions outside of labor that are constantly changing. The more thorough is the student's knowledge of the actual conditions of industry, the more correctly he can apprehend the relations of wages to other incomes, and the more wisely he will apply the abstract law to practical life. [Sidenote: Productivity of labor and diminishing returns of natural agents] 2. _The marginal productivity of labor is affected by the relative abundance and efficiency of natural resources._ If land suddenly becomes more abundant through the opening up of new continents, the lower grades of agents are sooner or later abandoned. Labor having more of a choice as to the place where it is to be used, spreads itself over the better grades and takes on a greater marginal productivity. The marginal unit of labor working on better soil than before produces more, and wages expressed in produce are higher. Ground rent, on the other hand, is less under these conditions. If, however, the land is fixed in area, and population increases, no other change taking place, the principle of diminishing returns applies. The marginal laborers (the last arrivals or the growing generation) being compelled to work with less efficient resources on a poorer quality of land, produce less than was the rule before, and a smaller product therefore is attributed to all the laborers of that grade. They get lower wages and more goes as rent to the owners of the land. By shifting of occupations this reduction may be somewhat moderated and equalized among the workers in other industries. In both these cases, wages vary more than does the physical amount of the total product. In the first case, wages are a larger proportion of a larger product; in the second case, the product is larger (there being more laborers) but wages are a smaller proportion of it. [Sidenote: The iron law of wages]