The tendency of the rate of profit to fall (TRPF) is a theory in the crisis theory of political economy, according to which the rate of profit—the ratio of the profit to the amount of invested capital—decreases over time. This hypothesis gained additional prominence from its discussion by Karl Marx in Chapter 13 of Capital, Volume III, but economists as diverse as Adam Smith, John Stuart Mill, David Ricardo and Stanley Jevons referred explicitly to the TRPF as an empirical phenomenon that demanded further theoretical explanation, although they differed on the reasons why the TRPF should necessarily occur.
Geoffrey Hodgson stated that the theory of the TRPF "has been regarded, by most Marxists, as the backbone of revolutionary Marxism. According to this view, its refutation or removal would lead to reformism in theory and practice". Stephen Cullenberg stated that the TRPF "remains one of the most important and highly debated issues of all of economics" because it raises "the fundamental question of whether, as capitalism grows, this very process of growth will undermine its conditions of existence and thereby engender periodic or secular crises."
Causal explanations
Karl Marx
In Marx's critique of political economy, the value of a commodity is the amount of labour that is socially necessary to produce that commodity. Marx argued that technological innovation enabled more efficient means of production. In the short run, physical productivity would increase as a result, allowing the early adopting capitalists to produce greater use values (i.e., physical output). In the long run, if demand remains the same and the more productive methods are adopted across the entire economy, the amount of labour required (as a ratio to capital, i.e. the organic composition of capital) would decrease. Now, assuming value is tied to the amount of labor necessary, the value of the physical output would decrease relative to the value of production capital invested. In response, the average rate of industrial profit would therefore tend to decline in the longer term.
It declined in the long run, Marx argued, paradoxically not because productivity decreased, but instead because it increased, with the aid of a bigger investment in equipment and materials.
The central idea that Marx had was that overall technological progress has a long-term "labor-saving bias", and that the overall long-term effect of saving labor time in producing commodities with the aid of more and more machinery had to be a falling rate of profit on production capital, quite regardless of market fluctuations or financial constructions.
Countertendencies
Marx regarded the TRPF as a general tendency in the development of the capitalist mode of production. Marx maintained that it was only a tendency, and that there are also "counteracting factors" operating which had to be studied as well. The counteracting factors were factors that would normally raise the rate of profit. In his draft manuscript edited by Friedrich Engels, Marx cited six of them:
More intense exploitation of labor (raising the rate of exploitation of workers). Reduction of wages below the value of labor power (the immiseration thesis). Cheapening the elements of constant capital by various means. The growth of a relative surplus population (the reserve army of labor) which remained unemployed. Foreign trade reducing the cost of industrial inputs and consumer goods. The increase in the use of share capital by joint-stock companies, which devolves part of the costs of using capital in production on others.
Nevertheless, Marx thought the countervailing tendencies ultimately could not prevent the average rate of profit in industries from falling; the tendency was intrinsic to the capitalist mode of production. In the end, none of the conceivable counteracting factors could stem the tendency toward falling profits from production.
Capital stock growth
In Adam Smith's TRPF theory, the falling tendency results from the growth of capital which is accompanied by increased competition. The growth of capital stock itself would drive down the average rate of profit.
Other influences
There could also be several other factors involved in profitability which Marx and others did not discuss in detail, including: