If the total number of alternatives is two, the method of majority decision is a social welfare function which satisfies Conditions 2–5 and yields a … - Kenneth Arrow

There are many unknowns in the creation and use of knowledge as a factor of production. Still, two main lessons stand out:
* Every country or firm must have education and training in technology and science, even if the research is not on par with that being conducted elsewhere. Knowledge cannot be absorbed unless some knowledge is already possessed.
* Countries and firms must be open to new ideas, have multiple sources of new ideas, and see that ideas are diffused. This point strongly argues for freedom of entry, even when it seems to forgo economies of scale.

As a general rule, the greater the uncertainty, the better to avoid large and irreversible commitments, to the extent that it is possible. When the famous 1930s gangster, Dutch Schultz, was dying, his incoherent last remarks were taken down by a stenographer. One of them was. "Don't make no bull moves." His words are a lesson for the kind of future that one might choose. Maintaining flexibility or keeping ones options open, is key in these matters.

Not only is it possible to devise complete models of the economy on hypotheses other than rationality, but in fact virtually every practical theory of macroeconomics is partly so based. The price- and wage- rigidity elements of Keynesian theory are hard to fit into a rational framework, though some valiant efforts have been made. … But if the Keynesian model is a natural target of criticism by the upholders of universal rationality, it must be added that monetarism is no better. I know of no serious derivation of the demand for money from a rational optimization. … The use of rationality in these arguments is ritualistic, not essential.