Usefulness depends on tractability.

Markets are not, in my opinion, a full solution to any problem. The obvious problem they don't meet is the concerns of the welfare of individuals who may get lost in the operation of the system - the distributional question. We've seen this growing as we go further and further toward a market ideology in the United States and the United Kingdom. We've seen a decline in the welfare of the working poor, leaving aside any other pathologies, just the working poor, a very distinct increase at the very top levels.

Knowledge is a free good. The biggest cost in its transmission is not in the production or distribution of knowledge, but in its assimilation. This is something that all teachers know.

From the time I first understood economic principles, I was always concerned also that any system be operated on an efficient basis, which meant decentralization because knowledge is not concentrated anywhere. It's based on motivation, and so these are the advantages of, say, the cautious case for capitalism, that the market system is efficient.

One way of looking at Impossibility Theorem is that we proposed some criteria for what a good system should be: what is it you want from a voting system, and impose some conditions. And then ask: can you have a voting system that guarantees that?

The intrinsic social structure, the family structure and so forth, is certainly in a very bad state. And I think that this is showing up in productivity. I think part of the reason, and I can't prove this, we're seeing a decline in some places is the breakup of the family, which is partly the result of an extreme form of individualism.

Unsolved problems, that's one of the great signs of progress in my opinion.