Uncertainty means that we do not have a complete description of the world which we fully believe to be true. - Kenneth Arrow

Ever since I encountered Hicks’s Value and Capital while I was still a graduate student, I had the aim of completing and extending his vision of the economic system in its purest form. This was not because I believed that the economic world was perfectly competitive or that it was clearly self-equilibrating; after all, Chamberlin, Robinson, and Keynes were dominant intellectual influences, and I had the even more powerful influence of the facts of massive unemployment and large corporations. But the idea that the economic world was a general system, with all parts interdependent, seemed (and seems) to me to be an essential of good analysis. I regret what appears to be a revival of single-market thinking both among monetarists and among some of the younger empirical analysts. Then as now, the only game in town that offered a general system of economic interdependence was general competitive equilibrium, an idea to which the name of Leon Walras is imperishably linked. At least, such a system would provide a starting point for analysis of the market’s imperfections.

I am old-fashioned enough to retain David Hume’s view that one can never derive “ought” propositions from “is” propositions. The two issues, method and value, are distinct.

Even Ricardo's most famous accomplishment, the law of comparative advantage in foreign trade, is incomplete, though not wrong.