bourgeoisie) who own the means of production and the vast majority of the population (the proletariat) who produce goods and services. Starting with the conjectural premise that social change occurs because of the struggle between different classes within society who are under contradiction against each other, a Marxist would conclude that capitalism exploits and oppresses the proletariat, therefore capitalism will inevitably lead to a proletarian revolution. In a socialist society, private property—in the form of the means of production—would be replaced by co-operative ownership. A socialist economy would not base production on the creation of private profits, but on the criteria of satisfying human needs—that is, production would be carried out directly for use. As Friedrich Engels said: "Then the capitalist mode of appropriation in which the product enslaves first the producer, and then the appropriator, is replaced by the mode of appropriation of the product that is based upon the nature of the modern means of production; upon the one hand, direct social appropriation, as means to the maintenance and extension of production on the other, direct individual appropriation, as means of subsistence and of enjoyment". Marxian economics and its proponents view capitalism as economically unsustainable and incapable of improving the living standards of the population due to its need to compensate for falling rates of profit by cutting employee's wages, social benefits and pursuing military aggression. The socialist system would succeed capitalism as humanity's mode of production through workers' revolution. According to Marxian crisis theory, socialism is not an inevitability, but an economic necessity. Classical Marxism is the economic, philosophical and sociological theories expounded by Marx and Engels as contrasted with later developments in Marxism, especially Leninism and Marxism–Leninism. Orthodox Marxism is the body of Marxism thought that emerged after the death of Marx and which became the official philosophy of the socialist movement as represented in the Second International until World War I in 1914. Orthodox Marxism aims to simplify, codify and systematize Marxist method and theory by clarifying the perceived ambiguities and contradictions of classical Marxism. The philosophy of orthodox Marxism includes the understanding that material development (advances in technology in the productive forces) is the primary agent of change in the structure of society and of human social relations and that social systems and their relations (e.g. feudalism, capitalism and so on) become contradictory and inefficient as the productive forces develop, which results in some