2. Without the theoretical difference between PL and UPL, there is no theory of surplus value and S/V. Hence no theory of class struggle and crisis. Hence, no Marxist socio-economics or economic sociology. Without Marxist socio-economics, no social science of capitalism.
Two problems with this kind of discussion are: 1. No one has published a non-tautological proof that capital exploits labor. This the category "exploitation" is defined and used in all kinds of ways. It is a tautological proof that SV is the difference between the value of labor power and the value of the product of labor; a non-tautological proof requires empirical observation of the labor market and exact nature of the wage bargain, that is, a proof that requires both sociological and economic observations.
2. In an article "Productive and Unproductive Labor" written long ago, published I think but am not sure in Politics and Society, I tried to pack more meaning into the categories PL and UPL, by arguing: 1. Productive labor is the productive consumption of laborpower (Marx). 2. Unproductive labor is the unproductive consumption of laborpower (Marx). 3. When workers open holes in the workday via struggle, "labor is unproductively consumed (Marx), that is, unproductive labor has a status within "class struggle theories of Marxism, as well as in political economy. Jim O'Connor