The legitimate purpose of abstraction in social science is never to get away from the real world but rather to isolate certain aspects of the real wo… - Paul Sweezy

Supply and demand will be in equilibrium only when the price of every commodity is proportional to the labor time required to produce it. Conversely prices proportional to labor times will be established only if the forces of competitive supply and demand are allowed to work themselves out freely. The competitive supply-and-demand theory of price determination is hence not only not inconsistent with the labor theory; rather it forms an integral, if sometimes unrecognized, part of the labor theory.

It must be emphasized, because the contrary has so often been asserted, that Marx was not trying to reduce everything to economic terms. He was rather attempting to uncover the true interrelation between the economic and the non-economic factors in the totality of social existence.

Discussions of methodology in economics, as in other fields, are likely to be tiresome and unrewarding. Nevertheless, to avoid the problem altogether is to risk serious misunderstanding.