The development of the productive forces has two aspects:
1. The growth of the number of workers incorporated into production at a given level of productivity;
2. The development of labour productivity amongst a given number of workers.
In a system in full expansion, one can see a combination of both. A system in crisis is a system which has reached it limits in both aspects at the same time.
We can speak of an ‘external limit’ to the expansion of a system (its incapacity to enlarge its field of action) and of an ‘internal limit’ (the incapacity to go beyond a certain level of productivity). Consider the case of the end of slavery, of the Roman Empire. The external limit was constituted by the material impossibility of enlarging the extent of the Empire. The internal limit was the impossibility of raising the productivity of the slaves without overthrowing the social system itself, without eliminating their status as slaves. For feudalism it was the end of land reclamation, the incapacity to find new arable lands, which acted as the external limit, while the internal limit was its inability to raise the productivity of the serfs, or of the individual artisan, without transforming them into proletarians, without introducing labour associated by capital: that is, without the overthrow of the feudal economic order.
The approach of these two types of limits are dialectically linked: Rome could not expand its empire indefinitely because of the limits of production; inversely, the more difficult it was to expand, the more it was obliged to develop its productivity, thus pushing it more rapidly towards its extreme limits. Likewise feudal reclamations were limited by the level of feudal techniques, while the scarcity of land encouraged more ingenuity in productive activities carried out in the towns and the countryside. This in turn pushed feudal productivity to the border of capitalism.
In the final analysis it is the limits on the level of productivity within the old society which lead it into the morass. It is this productivity which is the true measure of the level of development of the productive forces; it’s the quantitative expression of a certain combination of human labour and means of production, of living and dead labour .
To each stage of development of the productive forces, that is, at each overall level of productivity, there corresponds a certain type of relations of production. When this productivity approaches its last possible limits within the system which corresponded to it, and if the system is not overthrown, society enters into a phase of economic decadence. Then there is a snowball effect: the first consequences of the crisis transform themselves into factors accelerating the crisis. For example, at the end of Rome as well as in the decline of feudalism, the drop in revenues of the ruling class pushed the latter to reinforce the exploitation of the workforce to the point of exhaustion. The result in both cases was the growing apathy and discontent of the labourers, which only accelerated the decline in revenues.
Likewise the impossibility of incorporating new labourers into production forced society to support inactive strata who constituted yet another drain on revenues.
A similar phenomenon was the galloping devaluation of money at the end of the Empire as well as at the end of the Middle Ages: “Rome had hoped to cover its governmental expenses by increasing taxation, but when the proceeds proved insufficient it was necessary to resort to inflation (at the end of the Second Empire). This first expedient had to be repeated from time to time in the course of the third century, certain monies being devalued to 2 percent of their face value. The monetary unity of the Empire was destroyed; each town and each province issuing its own money”( Shepard B Clough, op cit, p 141).
And at the end of the Middle Ages: “In a world where the mass of money became insufficient, the wage-bill (of soldiers used for protection against robbery or in wars - ICC note) increased the need for precious metals; thus the temptation to overvalue the cash in circulation. The rulers used their authority to diminish the weight of coins, so that a coin valued at 2 sous henceforth contained less pure silver and more lead, but was now worth 3 sous. This was inflation!”( J Favier, op cit, p 127).
Parallel to these economic consequences the crisis causes a series of social convulsions which in their turn impede an already enfeebled economic life. The development of productivity systematically conflicts with existing social structures, rendering impossible any new development of the productive forces. the need to go beyond the old society is put on the agenda.
“A society never expires before all the productive forces contained within it have been developed” (Marx, op cit).
In fact it should be noted that no system has developed ALL the productive forces - in the proper sense of the term - which it may contain in theory.
On the one hand, the economic consequences that we have seen and the series of social catastrophes which the first great economic difficulties cause are so many fetters preventing the system really attaining its absolute limits. We must bear in mind that an economic system is the ensemble of relations of production that men have been led to establish, independently of their will and in accord with the level of productive forces, to PROVIDE FOR THEIR ECONOMIC NEEDS. Before the last instrument of production has seen the light of day, if production has started to grow less quickly than the needs of the population, the system loses its historic reason for existence, and everything in society tends to push against its confines.
On the other hand, under the pressure of the productive forces, the economic foundations of the new society begin to develop within the old. This only applies to past societies where the class which overthrew them was never the exploited class. Feudalism grew up within the Roman empire. The first feudal plantations in Rome were often headed by old members of the municipal senate put to flight by a state which made them responsible for the collection of taxes.
Likewise, at the end of feudalism, members of the nobility became businessmen, and in the towns - often in struggle against local lords - developed the first manufactories, prefiguring capitalism.
These first ‘centres of the future system’ (great Roman plantations, bourgeois towns) were mostly born as the result of the decomposition of the old system. They attracted all kinds of elements trying to escape the system. But from being the results of decadence, these centres quickly transformed themselves into factors that hastened it along.
Material conditions permit the passage to a new type of society, whose premises already exist within the old society, and their pressure is sufficient to begin the foundation of a new system.
“New relations of production have never been put into place before the material conditions of their existence has been discovered within the old society” (Marx, op cit).
It is not enough that production approaches its final limits within the old society. It is also necessary that the means to go beyond the latter already exist or are in the process of formation. When these two conditions are historically realised, society’s adoption of new relations of production is on the agenda. But the resistance of the old society (of the old privileged class, the inertia of customs and habits, ideologies, religion etc), and the gap that may exist between the realisation of these two conditions, means that such transformations do not take place in a progressive, linear manner, but through a series of regressions, catastrophes, and qualitative leaps.
The phase of decadence of a system is that period in which such a historic leap has not been made; it is the expression of a growing contradiction between the productive forces and the relations of production; it is the sickness of a body whose clothes have become too tight.
 It is this relation which under capitalism will be partially expressed by the organic composition of capital: c¼v constant capital over variable capital.