We have seen that there were critics of post-Ricardian trends, particularly as regards the theory of profits, who tried to carry Ricardian theory further and to turn it into a critique of Capital itself. These were writers and pamphleteers like Thomas Hodgskin and William Thompson and J. F. Bray and John Gray, to whom the name of ‘Ricardian Socialists’ has been given; and although they inhabited what Keynes, a century later, was to call the “underworld of heretics”, their significance did not go unnoticed by economists of gentry-breed in Dublin or Oxford. Although their audience was to be found in Mechanics Institutes and among incipient trade unions and radical fraternities, rather than in the cloisters of ancient universities, their actual or potential influence was evidently feared by writers such as Scrope and Read.

Hodgskin presented his rather undeveloped concept of exploitation from the standpoint of a believer in a Smithian ‘natural harmony’ of natural laws; and from this standpoint he was a critic of Ricardo, especially the latter's theory of wages and theory of rent. His claim that labour had a right to the whole produce, and that profit and rent were alike filched from labour, was essentially a natural right doctrine, such as Marx's surplus-value is commonly, but erroneously, interpreted as being. Natural right to property in the fruit of one's own labour was sharply contrasted with ‘the legal or artificial’ right of property to appropriate the product of the labour of others.