I think one of the things we learned from the physicists and also the theoretical biologists is the idea that when you're dealing with very complex s… - Kenneth Arrow

Krugman's whole attack is directed at a statement made neither by Arthur nor by Cassidy. Krugman has not read Cassidy's piece with any care nor has he bothered to review what Arthur has in fact said.

The problem of interpersonal comparison of utilities seems to bother economists more than philosophers. As already indicated, utility or satisfaction or any other similar concept appears in economic theory as an explanation of individual behavior, for example, as a consumer. Specifically, it is hypothesized that the individual chooses his consumption so as to maximize his utility, subject to the constraints imposed by his budget. But, for this purpose, a quantitatively measurable utility is a superfluous concept. All that is needed is an ordering, that is, a statement for each pair of consumption patterns as to which is preferred.

Finding out the prices of a large range of commodities is itself a costly enterprise, and knowledge of this fact by price setters is itself enough to create incentives for inefficient market behavior. If one individual has more information about the quality of a good than the second, the first may exploit the situation, and the second, distrusting him, may not take advantage of what is in fact a desirable trade.