James asked:
> So, I'd 
>like to ask, In what sense was the theory of demand and supply as an 
>explanation of market price determination a post-1850 development?
>


I believe that I answered this question, although not in the context in which you raise it. For Marshall, who adopted the real cost idea, there was not a lot of difference. But for Davenport, Knight, and, later, Mises; there was a world of difference. When one conceives of cost as opportunity cost (1892), the thoughtful mind is led away from an explanation of the price of a single good or resource and toward an explanation of how consumer wants, in a more general sense, get satisfied under market economy conditions. The culmination of the thought process is the recognition of the role of the entrepreneur (1914) and of the role of consumer sovereignty in the sense of a procedure of conceptualizing the outcome of economic interaction as opposed to an expression of the [methodologically unproductive] distinction between productive and unproductive "labor."

(It occurs to me that one might say that, in England, Marshall killed the propensity to extend demand and supply analysis into a theory of entrepreneurship. He used the undertaker to bury it.)
 
Pat Gunning