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.

Mathematicians themselves set up standards of generality and elegance in their exposition which are a bar to understand.

The world moves into the future as a result of decisions, not as a result of plans. Plans are significant only insofar as they affect decisions.

We are born to love, as we are born to breathe and eat and drink.

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.

Physicists can only talk to other physicists and economists to economists... sociologists often cannot even understand each other.

The organizer who creates roles, who creates the holes that will force the pegs to their shape, is a prime creator of personality itself. When we ask of a man, "What is he?" the answer is usually given in terms of his major role, job, or position in society; he is the place that he fills, a painter, a priest, a politician, a criminal.