The tendency of the rate of profit to fall (TRPF) is a hypothesis 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.