Exploitation in Capitalism: Marx’s Theory of Surplus Value

Why does a worker who produces goods worth thousands of rupees take home only a fraction of that value in wages? For Karl Marx, this gap was not an accident or a sign of stingy bosses. It was the engine of the entire capitalist system. His theory of surplus value, worked out across the three volumes of Capital, set out to explain exactly how profit is created and why Marx believed it amounts to the systematic exploitation of labour. Understanding this theory is essential to grasping his larger critique of capitalism and his prediction of its eventual collapse.

The starting point: the labour theory of value 🔗

Before we can understand surplus value, we need to understand where value comes from in the first place. Marx inherited and reworked the labour theory of value from classical economists like Adam Smith and David Ricardo. The core claim is straightforward: the value of any commodity is determined by the amount of socially necessary labour time required to produce it.

This means that the price of a chair, a phone, or a shirt is ultimately rooted in the human labour embodied in it, not in the soil, the machinery, or the market by itself. Classical economists used this idea to explain the “natural price” of goods and how the social product gets divided into wages, profit, and rent. Marx took the same starting point but pushed it in a radical direction, arguing that profit ultimately originates from the unpaid surplus labour of workers.

Labour versus labour power 🔗

Marx’s most important breakthrough was a subtle but powerful distinction between labour and labour power. This single idea is what makes the whole theory work, so it is worth slowing down here.

The capitalist does not actually buy a worker’s labour. If they did, and paid the full value of what that labour produces, there would be no profit and the arrangement would be obvious robbery. Instead, the capitalist buys labour power, which is the worker’s capacity to work for a given period. Like any other commodity, labour power has a value, and that value is set by the cost of reproducing it, meaning the food, shelter, clothing, and other necessities a worker needs to keep showing up to work day after day.

Here is the crucial point. The use value of labour power, what it can actually do once put to use, is its ability to create new value, including more value than it costs to maintain the worker. Surplus value is simply the difference between the total new value the worker creates and the value of their own labour power. This distinction, Marx insisted, is nothing mysterious. It is a plain description of a process that happens in millions of workplaces every single day.

How surplus value is produced 🔗

To see surplus value in action, Marx broke the capitalist’s investment into two parts. He called money spent on machinery, tools, and raw materials constant capital (symbol: c), because it transfers its existing value to the product without adding anything new. He called money spent on wages variable capital (symbol: v), because this is the part that expands. Only living labour creates fresh value.

A simple illustration from Marx makes this clear. Suppose a worker is hired for ₹100 and uses ₹1,000 worth of materials to produce something sold for ₹1,300. In this case ₹1,000 is constant capital, ₹100 is variable capital, and ₹200 is surplus value. The materials simply passed their value along. The surplus of ₹200 was added solely by the worker’s activity, yet it ends up in the capitalist’s pocket.

The working day, split in two 🔗

The mechanism becomes vivid when we look at the working day. Marx argued that the day divides into two parts: necessary labour time and surplus labour time. During necessary labour time, the worker produces value equal to their own wages. During surplus labour time, the worker keeps producing, but this additional value flows entirely to the capitalist.

Using one of Marx’s own examples from Capital, if a day’s labour power is worth five shillings and one working hour equals sixpence, the worker must labour ten hours to reproduce the value of their wages. If the working day is actually twelve hours, the extra two hours are pure surplus labour, handed over for free. The wage looks like payment for the whole day, but in reality it covers only the necessary portion. The rest is unpaid, and this unpaid labour is the secret source of profit.

Measuring exploitation: the rate of surplus value 🔗

Marx wanted to quantify exploitation, so he introduced the rate of surplus value, expressed as the simple ratio s/v, that is, surplus value divided by variable capital. Importantly, he treated this figure as identical to the rate of exploitation. The higher the ratio, the more unpaid labour the capitalist extracts relative to wages paid.

So in our earlier ten-hour example, where necessary labour was ten hours and surplus labour was two, the rate of exploitation would be relatively modest. But Marx showed that this rate could be pushed dramatically higher. The total value of a commodity, in his notation, is written as (c + v) + s, and the entire drama of capitalism lies in maximising that final term, s.

Two ways to squeeze more surplus 🔗

Marx identified two distinct strategies capitalists use to increase surplus value.

Absolute surplus value comes from simply extending the working day. By increasing the day from, say, eight to ten hours, the capitalist gains two extra hours of surplus value while paying the same wage. This was the brutal reality of early industrial capitalism, and it is why struggles over the length of the working day, weekly offs, and overtime have always been central to labour movements.

Relative surplus value is more sophisticated. Here the working day stays the same length, but the capitalist shrinks the necessary labour time. This is usually achieved by introducing new machinery and raising productivity, so that workers can reproduce the value of their wages in fewer hours, leaving more of the day as surplus. When the intensity of labour is raised through new technology or reorganisation, necessary labour time falls relative to surplus labour time, even if workers’ living standards stay the same. Modern productivity drives, automation, and efficiency targets are, in Marx’s framework, all attempts to extract relative surplus value.

From surplus value to profit, rent, and interest 🔗

One of Marx’s bolder claims was that surplus value is the hidden source of all property income, not just industrial profit. The profit of the factory owner, the interest of the banker, and the rent of the landlord are, in his view, simply different slices of the same pie, which was baked entirely by labour.

Marx argued that the competitive marketplace creates a kind of illusion. It appears that land produces rent and capital produces profit, as if money and machines were themselves productive. But this surface appearance, he claimed, conceals the fact that labour is the only socially relevant source of output. Profit, interest, and rent are not rewards generated by capital or land on their own. They are portions of surplus labour redistributed among different sections of the propertied class. Marx considered this analysis of surplus value, treated independently of its particular forms, to be among his most important contributions.

Why the system heads toward crisis 🔗

Marx did not stop at explaining exploitation. He argued that the very pursuit of surplus value drives capitalism toward instability. As capitalists compete, they invest more and more in machinery, that is, in constant capital, relative to living labour. This raises what Marx called the organic composition of capital.

Here lies a deep contradiction. Living labour is the sole source of surplus value, yet the drive to accumulate keeps replacing workers with machines. The rate of profit, which Marx defined as s/(c + v), therefore faces a downward pressure. As the constant capital in the denominator grows faster than the surplus value that living labour can create, the rate of profit tends to fall. Capital, in chasing ever more surplus value, ends up undermining its own source of profit.

A tendency, not an iron law 🔗

It is worth being precise here, because this part of Marx is often misunderstood. Marx described this as a tendency of the rate of profit to fall, not an automatic, uninterrupted decline. He explicitly identified counteracting influences that can periodically halt the downward slide, such as raising the rate of exploitation, cheapening the elements of constant capital, or expanding into new markets. The rate of profit can in fact rise for considerable stretches of time, which is exactly why crises arrive in waves rather than as a single final collapse.

Exploitation, inequality, and revolution 🔗

For Marx, the steady accumulation of surplus value in fewer and fewer hands meant that wealth and poverty would grow together at opposite poles of society. The capitalist class would expand its riches while the working class, the proletariat, remained dependent on selling its labour power for wages that never captured the full value it created.

This was not merely an economic observation but the foundation of his political conclusion. Marx held that the rate of surplus value is, from the worker’s side, simply the rate of exploitation, which made surplus value the real motor of class struggle. As crises deepened and inequality widened, he predicted that the proletariat would eventually recognise the system as the source of its condition and move to overthrow it, replacing private appropriation of surplus value with collective ownership of the means of production.

Whether or not one accepts Marx’s predictions, his theory of surplus value remains a strikingly clear attempt to answer a question that still matters: when value is created at work, who gets to keep it, and why? It reframes profit not as a neutral reward for risk or innovation but as a relationship between classes. It also has its critics, since from the late nineteenth century mainstream economics largely replaced the labour theory of value with theories based on marginal utility, locating value in consumer demand rather than labour alone.

What do you think? If value really is created mainly by labour, how should the gains from rising productivity and automation be shared between workers and owners today? And do you find Marx’s distinction between labour and labour power convincing as an explanation of where profit comes from?

References

1. https://en.wikipedia.org/wiki/Labor_theory_of_value
2. https://internationalviewpoint.org/Marx-s-Theory-of-Surplus-Value
3. https://en.wikipedia.org/wiki/Constant_and_variable_capital
4. https://www.marxists.org/archive/marx/works/1867-c1/ch12.htm
5. https://la.utexas.edu/users/hcleaver/357k/357ksg09.html
6. https://liberationschool.org/03-what-is-surplus-value-html/
7. https://journals.sagepub.com/doi/10.1177/03098168231199913
8. https://criticofpolecon.substack.com/p/what-karl-marxs-value-theory-is-really
9. https://thetricontinental.org/dossier-notebook-4-economic-crisis/
10. https://marxist.com/the-capitalis-and-the-tendency-of-the-rate-of-profit-to-fall.htm