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 evolutionary vision is agnostic in regard to systems in the universe of greater complexity than those of which human beings have clear knowledge. It recognizes aesthetic, moral, and religious ideas and experiences as a species, in this case of mental structures or of images, which clearly interacts with other species in the world's great' ecosystem.

Know this: though love is weak and hate is strong, Yet hate is short, and love is very long.

One advantage of exhibiting a hierarchy of systems in this way is that it gives us some idea of the present gaps in both theoretical and empirical knowledge. Adequate theoretical models extend up to about the fourth level, and not much beyond. Empirical knowledge is deficient at practically all levels.

Knowledge exists in minds, not in books. Before what has been found can be used by practitioners, someone must organize it, integrate it, extract the message.

The evolutionary vision is agnostic in regard to systems in the universe of greater complexity than those of which human beings have clear knowledge.

As far as many statistical series that are related to activities of mankind are concerned, the date that divides human history into two equal parts is well within living memory. The world of today is as different from the world I was born in as that world was from Julius Caesar s. I was born in the middle of human history, to date, roughly. Almost as much has happened since I was born as happened before.