Dialectical materialism has guided his subsequent work, notably the theoretically sophisticated "Limits to Capital" (1982), which furthers the radical geographical analysis of capitalism, and several books on urban processes and urban life have followed it. In ‘Limits to Capital’ Harvey expanded and innovated Marxist theory with respect to the functioning of money and finance, and the ‘spatial moment’ in the unfolding of capitalist crisis formation. "The Condition of Postmodernity" (1989), written while a Professor at Oxford, was a best-seller (the London "The Independent" named it as one of the fifty most important works of non-fiction to be published since 1945, and it is cited 30,000 times by 2017). It is a materialist critique of postmodern ideas and arguments, suggesting these actually emerge from contradictions within capitalism itself. "Justice, Nature and the Geography of Difference" (1996) focuses on social and environmental justice (although its dialectical perspective has attracted the ire of some Greens). "Spaces of Hope" (2000) has a utopian theme and indulges in speculative thinking about how an alternative world might look.