What was Paulus's "famous definition of price"? Schumpeter (1912 [1954]) mentions 


  the famous definition of price by Paulus.


What does this refer to?
Julius Paulus Prudentissimus, circa 230 CE

"material was selected which, being given a stable value by the state, avoided the problems of barter by providing a constant medium of exchange. 
That material , struck in due form by the mint, demonstrates its utility and title not by its substance as such but by its quantity, so that no longer are the things exchanged both called wares but one of them is termed the price.
An today its is a matter for doubt  whether one can talk of sale when no money passes. "

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