Marx used the terms surplus and exploitation in a pejorative sense. He strongly believed that the income distribution at the time was unfair and that the institutions that led to this unfairness deserved to be called exploitative. Most modern economists see such judgments as going beyond the role of economists as economists. They try to separate normative judgments from positive analysis. But even in terms of normative judgments, they question the value of the exploitation concept. They see human nature as generally exploitative and see the market as based on the concept of mutual exploitation. Abba Lerner summarized this view nicely: in capitalism man exploits man; in socialism It is the other way around.