Was in a conversation with someone who argued that slaves don't produce surplus value, that surplus value is unique to a worker-owner relation as in liberalism. Is anyone familiar with this idea? It didn't make a great deal of sense to me. One would think that slaves would give you as much if not more surplus value than workers you have to pay.
Note that "slaves would give you as much if not more surplus value than workers you have to pay" is one of the central problems here. They surely would give more surplus value in %, but in absolute values they would only do so in very primitive level of development, and even then not necessarily since even in antiquity slave labour was often considered inefficient.
Marx write more of this in Capital iirc.