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

General Systems Theory is a name which has come into use to describe a level of theoretical model-building which lies somewhere between the highly generalized constructions of pure mathematics and the specific theories of the specialized disciplines. Mathematics attempts to organize highly general relationships into a coherent system, a system however which does not have any necessary connections with the "real" world around us. It studies all thinkable relationships abstracted from any concrete situation or body of empirical knowledge.

The most fundamental form of integrative power is the power of love.

The right to have children should be a marketable commodity, bought and traded by individuals but absolutely limited by the state.

It is clear that the building of models is not a purely mechanical process but requires skill of a high order - not merely mathematical skill but a sensitivity to the relative importance of different factors and a critical, almost an artistic, faculty in the selection of behaviour equations which are reasonable, tentative hypotheses in explaining the behaviour of actual economies.

It is absurd to suppose we can think of nature as a system apart from knowledge, for it is knowledge that is increasingly determining the course of nature.

Economics, we learn in the history of thought, only became a science by escaping from the casuistry and moralizing of medieval thought.