[This book] is intended as a text from which the student can learn and the teacher can teach the methods and results of economic analysis. It also se… - Kenneth E. Boulding

One of the most important skills of the economist, therefore, is that of simplification of the model. Two important methods of simplification have been developed by economists. One is the method of partial equilibrium analysis (or microeconomics), generally associated with the name of Alfred Marshall and the other is the method of aggregation (or macro-economics), associated with the name of John Maynard Keynes.

The should not be confused with the profit system. By the profit system, of course, we mean the institution of private property in capital goods and the free private enterprise that goes along with it. There is no reason why the "profit motive" should be necessarily connected with the profit system. In a profit system there is nothing to prevent anyone acting on altruistic lines; there is no law that says a businessman must maximize his profits. If a businessman chose to operate with outputs, prices, and wages that yielded him a smaller profit than the maximum, but which he felt were socially more desirable, there is nothing in the profit system that would prevent him from doing this. Nothing in the profit system would prevent the most ardent liberal from refusing an increase in wages, or from accepting an unpleasant and poorly paid job. At the other extreme, there is nothing in a communist system that would do away with the profit motive, or the "advantage motive."

The use of isoquants to describe the production function did not develop to any great extent until the thirties.