Roughly speaking, it is the extra goods produced above the amount needed for a community of workers to survive at its current standard of living.
Marx first began to work out his idea of surplus product in his 1844 notes on James Mill's Elements of political economy.
This raised the difficult problem of how, then, one could devise a system for grossing and netting incomes & expenditures to estimate only the value of the new additional wealth created by a country.
For centuries, there was little agreement about that, because rival economists each had their own theory about the real sources of wealth-creation[6]—even if they might agree that the value of production must equal the sum of the new revenue which it generates for the producers.
The Physiocratic school, for example, believed that all wealth originated from the land, and their social accounting system was designed to show this clearly.
For most of the history of urban civilisation, excess foodstuffs were the main basis of the surplus product, whether appropriated through trade, tribute, taxation, or some other method.
In this context, Marx distinguishes between the physical minimum requirements for the maintenance of human life, and a moral-historical component of earnings from work.
Once some reserves and surpluses exist, tribes can diversify their production, and members can specialise in producing tools, weapons, containers, and ornaments.
In addition, a secure surplus product makes possible population growth, i.e. less starvation, infanticide, or abandonment of the elderly or infirm.
[21] Archaeologist Geoffrey Dimbleby comments: "It has been calculated that if man had never progressed beyond the hunting and food-gathering stage, the maximum population which the world's surface could support at any one time would be 20–30 million people.
[25] Although there is considerable controversy and speculation among archaeologists about how exactly these early rulers came to power[26] (often because of a lack of written records), there is good evidence to suggest that the process does occur, particularly in tribal communities or clans which grow in size beyond 1,500 or so people.
To maintain social order and enforce a basic morality among a growing population, a centralized state apparatus emerges with soldiers and officials, as a distinct group in society which is subsidized from the surplus product, via taxes, tributes, rents and confiscations (including war booty).
In turn, this gives rise to a moral or religious ideology which justifies superior and inferior positions in the division of labour, and explains why some people are naturally entitled to appropriate more resources than others.
Archaeologist Chris Scarre comments: "There has been some debate as to whether states should be considered beneficent institutions, operating for the good of all, or whether they are essentially exploitative, with governing elites gaining wealth and power at the expense of the majority.
"[28]Archaeologist Bruce G. Trigger comments: "It appears that, regardless of the agricultural regime followed, between 70 and 90 percent of the labour input in early civilizations was, of necessity, devoted to food production.
Thus, society has hitherto always developed within the framework of a contradiction—in antiquity the contradiction between free men and slaves, in the Middle Ages that between nobility and serfs, in modern times that between the bourgeoisie and the proletariat.
Which of those possibilities have been realised is not just a question of technique or productivity, but also of the assertion of power, ideology, and morals within the prevailing system of social relations governing legitimate cooperation and competition.
[35] In his famous book Capital in the Twenty-First Century, Thomas Piketty suggests that if present trends continue, there will be an even more gigantic concentration of wealth in the future.
Economic historian Paul Bairoch comments: "...in traditional societies the average agricultural worker produced an amount of foodstuff only about 20 to 30% in excess of his family's consumption.
These percentages—this 20 to 30% surplus—acquire special meaning if we take into account a factor often omitted from theories of economic development, namely, the yearly fluctuations of agricultural yields, which even at a national level could amount to an average of over 25%.
The consequent increase in productivity led in the space of 40 to 60 years to the transition from an average surplus of the order of 25% to something more like 50% and over, thus surpassing—for the first time in the history of mankind—what might be called the risk-of-famine limit; in other words, a really bad harvest no longer meant, as in the past, serious shortage or actual famine.
20th century experience with economic management shows that there is a broad scala of possibilities here; if some options are chosen, and others not, this has more to do with who holds political power than anything else.
The magnitude of the surplus product can be estimated in stocks of physical use-values, in money prices, or in labour hours.
Marxian theory suggests decadence involves a clear waste of a large part of the surplus product from any balanced or nuanced human point of view, and it typically goes together with a growing indifference to the wellbeing and fate of other human beings; to survive, people are forced to shut out from their consciousness those horrors which are seemingly beyond their ability to do anything about anymore.
[42] According to Marxian theory,[43] decaying or decadent societies are defined mainly by the fact that: Marxian scholars such as Ernest Mandel argued this condition typically involves a stalemate in the balance of power between social classes, none of which is really able to assert its dominance, and thus able to implement a constructive programme of action that would ensure real social progress and benefit the whole population.
According to Herbert Marcuse, a society is "sick" if its basic institutions and relationships are such that they make it impossible to use resources for the optimal development of human existence.
[44] However, there is a lot of controversy among historians and politicians about the existence and nature of decadence, because value judgements and biases about the meaning of human progress are usually involved.
That it was technically feasible for them to produce such a surplus is shown by the fact that, under the stimulus of European settlers' desire for food, a number of tribes did raise manioc in amounts well above their own needs, for the purpose of trading.
Income growth can, ultimately, only occur if the total stock of assets available for distribution itself grows, as a result of more being produced than existed before.
The more the trading network then expands, the more complex and specialized the division of labour will become, and the more products people will produce which are surplus to their own requirements.