Karl Popper was a great philosopher who solved the problem of induction and who shed light on many philosophical problems related to freedom. Popper showed that people learn through critical thought and discussion, not by building their views on non-existent secure foundations. Karl Marx was an intellectual lightweight whose utter misunderstanding of economics, his antisemitism and his worship of violence combined to form a poisonous brew that inspired all the terrible tyrants of the twentieth century from Hitler to Stalin.
Nevertheless, when BBC Radio 4 held a poll about who is the greatest philosopher, Marx was at number 1 and Popper was at number 10.
Why do so many people celebrate Marx? Marx was only one in a long line of philosophers who advocated socialism - the idea that people should collectively own property. But people cannot collectively own property. A given piece of property can only be put to a finite number of non-conflicting uses, and people are fallible, which is why they disagree. When people practise capitalism they decide how property will be used through agreements to which they subscribe voluntarily. Socialists and other opponents of capitalism license one particular group to use violence, or the threat thereof, to steal property from another. Favouring one group through violence prevents critical discussion of different ways to use property, which is anti-rational. Popper argued that we should have an open society in which people are free to criticise and work for the alteration of current institutions through reason and persuasion. Marx's contribution to this debate was to say that logic was a creation of the bourgeoisie and so logic is an evil tool of oppression. The workers, Marx said, had a different logic. When Marx had thrown logic out of the window he could say anything he liked and so was free to argue for socialism. Many of Marx's intellectual descendants have used Marx's argument against bourgeois logic to say their opponents are bourgeois and therefore necessarily wrong, without bothering to address their arguments. Thus Marx provided socialists with a way to cut short debates that they would have lost if they had stuck to rational discussion. That is why so many socialists love Marx: he gave them an excuse for their intellectual and moral irresponsibility. If our readers want an example of the sort of confusion that Marx's philosophy helped to encourage, we urge them to listen to the discussion on the programme that announced the results.
People can only really use Marx's philosophy to entrench error. However, we can use Popper's insights on knowledge and the open society to puncture the pretensions of dogmatic philosophers, illiberal governments and tyrants, and to understand the nature of knowledge and freedom. Karl Popper and Karl Marx have the same first name, but there the similarity ends. .