Value is defined here as "indirectly social labor," i.e., labor recognized as socially useful through the sale of the product. This exclusive criterion leads to the inclusion in the concept of commodity, alongside material goods, of all services (on condition that they are sold). The criterion of indirectly social work calls into question : 1) the traditional distinction between production activities and circulation activities (insofar as there is sale, both activities produce commodities and value) ; 2) the traditional conception of more skilled or more intensive labor (these do not create more value than average labor) ; 3) the traditional conceptions of the "value of labor power" and of the relations between this and the monetary wage. The non-conventional views adopted combine the advantages of rigor and simplicity : on the one hand, they make the theoretical approach more precise and coherent ; on the other hand, some of these views have the additional advantage of simplifying the theory and allowing a much simpler quantification of several basic concepts.