Pierre-Joseph Proudhon (1809-1865) was a French mutualist political philosopher of the socialist tradition. He was the first individual to call himself an "anarchist" and is considered among the first anarchist thinkers. Proudhon is most famous for his assertion that "Property is theft!," in What is Property?; or, An Inquiry into the Principle of Right and Government. The publication of What is Property? attracted the attention of the French authorities, and also of Karl Marx who started up a correspondence with Proudhon. The two men influenced each other and their friendship ended completely when Marx wrote a response to Proudhon's The System of Economic Contradictions; or, The Philosophy of Poverty entitled The Poverty of Philosophy. Their dispute was one of the origins to the split between the anarchist and marxist wings in the International Working Men's Association. In his earliest works, Proudhon analyzed the nature and problems of the capitalist economy. While deeply critical of capitalism, he also objected to those contemporary socialists who idolized association.