Thus the general supply of products may alternate periodically between shortage and surplus relative to the social demand. Herein lies the peculiar character of reproduction in a capitalist society, which differs from all other known forms of production. In the first place, every branch of production develops independently within certain limits, in a way that leads to periodical interruptions of production of shorter or longer duration. Secondly, the individual branches of reproduction show deviations from social requirements amounting to all-round disparity and thus resulting in a general interruption of reproduction. These features of capitalist reproduction are quite characteristic. In all other economic systems, reproduction runs its uninterrupted and regular course, apart from external disturbance by violence. Capitalist reproduction, however, to quote Sismondi's well-known dictum, can only be represented as a continuous sequence of individual spirals. Every such spiral starts with small loops which become increasingly larger and eventually very large indeed. Then they contract, and a new spiral starts again with small loops, repeating the figure up to the point of interruption. This periodical fluctuation between the largest volume of reproduction and its contraction to partial suspension, this cycle of slump, boom, and crisis, as it has been called, is the most striking peculiarity of capitalist reproduction. It is very important, however, to establish quite firmly and from the very outset that this cyclical movement of boom, slump, and crisis, does not represent the whole problem of capitalist reproduction, although it is an essential element of it. Periodical cycles and crises are specific phases of reproduction in a capitalist system of economy, but not the whole of this process. In order to demonstrate the pure implications of capitalist reproduction we must rather consider it quite apart from the periodical cycles and crises. Strange as this may appear, the method is quite rational; it is indeed the only method of inquiry that is scientifically tenable. In order to demonstrate and to solve the problem of pure value we must leave price fluctuations out of consideration. The approach of vulgar economics always attempts to solve the problem of value by reference to fluctuations in demand and supply. Classical economists, from Adam Smith to Karl Marx, attack the problem in the opposite way, pointing out that fluctuations in the mutual relation between demand and supply can explain only disparities between price and value, not value itself. In order to find the value of a commodity, we must start by assuming that demand and supply are in a state of equilibrium, that the price of a commodity and its value closely correspond to one another. Thus the scientific problem of value begins at the very point where the effect of demand and supply ceases to operate.