Herr Duehring finds competition to be the stumbling block in the way of his comprehension. He cannot understand how competing entrepreneurs can manage to sell the entire product of labor including the surplus product for so much more than the natural cost of production. Here again that "force" of his which, in his estimation, is the very evil thing, comes into play. According to Marx, the surplus product does not have any cost of production, it is the part of the product which costs the capitalist nothing. If the entrepreneurs were to sell the surplus product at its real cost of production they would have to give it away. Is it not a fact that the competing entrepreneurs really sell the product of labor every day at its natural cost of production? According to Herr Duehring the cost of production consists "in the expenditure of labor or force and therefore in the last analysis must be measured by cost of maintenance," and therefore, in present day society, is to be estimated at the cost of the raw material, instruments of labor and actual wages paid in distinction to taxation, profit and compulsory raising of prices. It is well recognised that in modern society the competing entrepreneurs do not sell their wares at the natural cost of production but calculate on a profit and generally get it. This question which Herr Duehring fancies will level the walls of Marxism as the blast of Joshua did those of Jericho is a question which the economic doctrines of Duehring have to meet also. "Capitalistic property," he says, "has no practical value and only realises itself because it implies the exercise of indirect power over man. The testimony to the existence of this force is capitalistic profit, and the amount of this latter depends upon the extent and intensity of the power of 'force.'... Capitalistic profit is a political and social institution which manifests itself very strongly as competition. The entrepreneurs take their stand on this relation and each one of them maintains his position. A certain amount of profit is a necessity of the dominant economic condition."