[In science any model depends on a pre-chosen taxonomy] a set of classifications into which we divide the enormous complexity of the real world... Land, labor, and capital are extremely heterogeneous aggregates, not much better than earth, air, fire, and water.

The concept of need is often looked upon rather unfavorably by economists, in contrast with the concept of demand. Both, however, have their own strengths and weaknesses. The need concept is criticized as being too mechanical, as denying the autonomy and individuality of the human person, and as implying that the human being is a machine which "needs" fuel in the shape of food, engine dope in the shape of medicine, and spare parts provided by the surgeon.

Economists are like computers. They need to have facts punched into them.

Physicists only talk to physicists, economists to economists-worse still, nuclear physicists only talk to nuclear physicists and econometricians to econometricians. One wonders sometimes if science will not grind to a stop in an assemblage of walled-in hermits, each mumbling to himself words in a private language that only he can understand.

[The notion of equilibrium] is a notion which can be employed usefully in varying degrees of looseness. It is an absolutely indispensable part of the toolbag of the economist and one which he can often contribute usefully to other sciences which are occasionally apt to get lost in the trackless exfoliations of purely dynamic systems.

It [knowledge] is clearly related to information, which we can now measure; and an economist especially is tempted to regard knowledge as a kind of capital structure, corresponding to information as an income flow. Knowledge, that is to say, is some kind of improbable structure or stock made up essentially of patterns - that is, improbable arrangements, and the more improbable the arrangements, we might suppose, the more knowledge there is.

We should always bear in mind that numbers represent a simplification of reality.