4) To these difficulties is added still another, which increases even more as soon as the various component parts of surplus-value appear in the form of mutually independent revenues. This difficulty consists in the definite designations of revenue and capital interchanging, and altering their position, so that they seem to be merely relative determinations from the point of view of the individual capitalist and to disappear when the total process of production is viewed as a whole. For instance, the revenue of the labourers and capitalists of Class I, which produces constant capital, replaces in value and substance the constant capital of the capitalists of Class II, which produces articles of consumption. One may, therefore, squeeze out of the dilemma by remonstrating that what is revenue for one is capital for another and that these designations thus have nothing to do with the actual peculiarities of the value components of commodities. Furthermore: commodities which are ultimately destined to form the substantive elements of revenue expenditure, that is, articles of consumption, pass through various stages during the year, e.g., woollen yarn, cloth. In one stage they form a portion of constant capital, in the other they are consumed individually, and thus pass wholly into the revenue. One may therefore imagine along with Adam Smith that constant capital is but an apparent element of commodity-value, which disappears in the total pattern. Thus, a further exchange takes place of variable capital for revenue. The labourer buys with his wages that portion of commodities which form his revenue. In this way he simultaneously replaces for the capitalist the money-form of variable capital. Finally: one portion of products which form constant capital is replaced in kind or through exchange by the producers of constant capital themselves; a process with which the consumers have nothing to do. When this is overlooked the impression is created that the revenue of consumers replaces the entire product, i.e., including the constant portion of value.