This selection of Marx's works edited by McClellan is wide enough to enable one to determine Marx's importance as a political thinker. Engels forever saw Marx's central achievement as "scientific socialism", but Marxism is not a science for its predictions are inaccurate. Marx wrongly predicted that workers would remain close to subsistence level, with many reduced to "pauperism". He was wrong to predict inexorably falling profits. He thought society would divide into just two classes but failed to see the rise of the managerial class and white collar workers in general. He predicted revolutions in advanced countries, but revolutions have been in backward countries such as Russia and China and Marxist only in name.
If Engels was wrong did Marx contribute anything of lasting significance? What about historical materialism? Engels compared Marx's "law of development of human history" with Darwin's "law of development of organic nature." The theory supposes that economic relations provide the substructure of society which determines the nature of the "superstructure", i.e. the law, form of government, culture etc. The theory of the dialectic used in this way has been discredited, and too many of Marx's followers adopted a crude economic determinism. However, a refined historical materialism helps us to understand that many institutions, ideas and events are at least influenced by economic matters. The European Reformation and the English Civil War are among events illuminated by the kernel of truth in historical materialism.
The theory of the class struggle is inextricably interwoven with historical materialism, for it is through the class struggle that history unfolds. Much of what Marx wrote on class in now seen as defunct, and critics disagree with Marx's use of class primarily as an economic group. However, Marx's theory that all forms of inequality can be reduced to social class, and that classes form the only significant social groups in society, comprises one of the two theories (Weber's being the other) that now dominate modern thinking on class. This is a measure of Marx's continuing importance as an analyst of class.
Marx's theory of alienation has risen in critical esteem as scientific socialism has declined. Alienation means that people are unable to derive satisfaction from their work, or from the products of their labour. Marx supposed that alienation arose from an economic system involving the exchange of goods, for the goods produced became mere "commodities" for sale rather than the means to "self-realisation". Marx observed that two features of modern industry - mechanisation and specialisation - further increase alienation, but believed that it is capitalism itself that is more important. In this he has been often criticised but alienation is an important concept and like other worthwhile theories has stimulated thought and led to modified alienation theories such as those of Gorz and Marcuse, whose theories encompass leisure as well as work, such that under capitalism people are alienated from both work and leisure.
Also significant is Marx's view of human nature, a key element in political thought. Marx supposed that human nature is malleable, altering according to socio-economic conditions in each time-period. Few people now agree with Marx that human nature is as pliable as he supposed but almost all agree with him that human nature can and does change according to circumstances.
Finally there is Marx's critique of the liberal conception of freedom. The mid-nineteenth century was dominated by the liberal concepts of negative liberty, the minimal state and laissez-faire economics. Marx, however, saw that actions that are rational and utility-maximising for individuals could harm the interests of society as a whole. Take the vexed issue of private versus public transport. The M25 into London is choked every morning with commuter traffic. Buses could complete the journey in a fraction of the time (and assist commercial transport to the benefit of the whole economy). An individual can use a bus, but whilst there are so many cars the bus is no quicker and less convenient. The liberal conception of freedom has led to a paradox: we have each chosen in our own interests, but the result is in no one's interest. Individual rationality, collective irrationality. Marx saw that capitalism involved this sort of collective irrationality. The problem, of course, is how to persuade people to cooperate for the common good (to use the bus in the above example) without unacceptable coercion, for it is in the interests of each individual for others to participate in the collective action whilst he remains a free-rider. Nevertheless, this in no way invalidates the force of Marx's critique of liberal freedom.