Andreas Loibl All the previous revolutions, as has already noted by Marx and Engels. have been the revolutions of the minority in the interest of new minority competing against the old minority leading to transition from one class society to another with the transformations in the forms of exploitation and domination. You are right in that that the present ruling classes cant calculate 7 years working period like the slave owners in the early 18th century, which prepare a high skilled worker. e.g. a software engineer with 20 years of "education", training the movement of his/her mind in a particular way, caging it in the paradigm of the epochal ideology -- "the idea of the age" -- "the ruling class ideas"; -- "the ruling ideas" that I call the epochal consciousness. The American ruling classes, till the first of of the 18th century when the colonizers of the north Americas registered their presence as power to reckon with on the world's economic map, did not depend on slave labor but on the indentured labor from their fatherland itself . With enslaved Africans, yet to acclimatize with the new environs, did not live longer and hence were costlier (less profitable). Once slaves started living longer, and news of inhuman treatment of indentured laborers back home impeded the supply of fresh indentured labor, the slave labor became the major source of surplus creation in return of meager means subsistence to reproduce slave labor. To justify the slavery, the pioneers constructed the ideology of RACE to create a superficial contradiction to blunt the edge of the major -- economic -- contradiction. The founders held the statue of liberty in one hand and the purse of the profit from slave trade in another reflecting the duality of capitalism, which is a bastard system in the sense that it never does what it professes and never says what it does. Totally agree with you that bourgeois freedom is of a worker is an illusion. Sorry for diverting from the main point of constant and variable capital discussion. In my opinion, that still holds true because machines cant themselves add value to the raw material, it is the only labor that by being consumed by the machines to act upon the raw material, adds value to the commodity and the value and the surplus value, thus can be genuinely measured only in terms of labor embodied in the commodity produced in the labor process.