He influenced not only immediate successors such as Richard Cantillon but also some of the greatest minds in economics, including Adam Smith and John Maynard Keynes. With Adam Smith, he shared a world view that believed in a harmonious natural world. The parallels in their canons of taxation epitomise their joint belief in natural liberty and equality. They both saw the benefits of specialisation and the division of labour. Furthermore, Smith and Petty developed labour theories of value, as did David Ricardo, Henry George, and Karl Marx in the 19th century.