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.

In calling society an ecological system we are not merely using an analogy; society is an example of the general concept of an "ecosystem" that is, an ecological system of which biological systems - forests, fields, swamps - are other examples.

The love of God again makes us free, for it draws us to set a low value on those things wherein we are subject to others - our wealth, our position, our reputation, and our life - and to set a high value on those things which no man can take from us - our integrity, our righteousness, our love for all men, and our communion with God.

The thing that distinguishes social systems from physical or even biological systems is their incomparable (and embarrassing) richness in special cases. Generalizations in the social sciences are mere pathways which lead through a riotous forest of individual trees, each a species unto itself. The social scientist who loses this sense of the essential individuality and uniqueness of each case is all too likely to make a solemn scientific ass of himself, especially if he thinks that his faceless generalizations are the equivalents of the rich vareity of the world.

At the opposite pole from the gift is tribute - that is, a grant made out of fear and under threat. A threat is a statement of the form "you do something that I want or I will do something that you do not want.

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.

In 1859 the human race discovered a huge treasure chest in its basement. This was oil and gas, a fantastically cheap and easily available source of energy. We did, or at least some of us did, what anybody does who discovers a treasure in the basement - live it up, and we have been spending this treasure with great enjoyment