The three forms (I) M ... M' (II) P ... P, and (III) C' ... C', present the following distinctions: in form II, P ... P, the renewal of the process, the process of reproduction, is expressed as a reality, while in form I only as a potentiality. But both differ from form III in that with them the advanced capital-value — advanced either in the form of money or of material elements of production — is the starting-point and therefore also the returning point. In M ... M' the return is expressed by M' = M + m. If the process is renewed on the same scale, M is again the starting-point and m does not enter into it, but shows merely that M has self-expanded as capital and hence created a surplus-value, m, but cast it off. In the form P ... P capital-value P advanced in the form of elements of production is likewise the starting-point. This form includes its self-expansion. If simple reproduction takes place, the same capital-value renews the same process in the same form P. If accumulation takes place, then P' (equal in magnitude of value to M', equal to C') reopens the process as an expanded capital-value. But the process begins again with the advanced capital-value in its initial form, although with a greater capital-value than before. In form III, on the contrary, the capital-value does not begin the process as an advance, but as a value already expanded, as the aggregate wealth existing in the form of commodities, of which the advanced capital-value is but a part. This last form is important for Part III, in which the movements of the individual capitals are discussed in connection with the movement of the aggregate social capital. But it is not to be used in connection with the turnover of capital, which always begins with the advance of capital-value, whether in the form of money or commodities, and which always necessitates the return of the rotating capital-value in the form in which it was advanced. Of the circuits I and II, the former is of service in a study primarily of the influence of the turnover on the formation of surplus-value and the latter in a study of its influence on the creation of the product.