In a democracy people are free to express their opinions and question those of others. This is an important personal freedom, and also essential to the very idea of government by discussion. But it has also been held to be instrumentally important because in open public debate true ideas will conquer false ones by their merit, and the people will see the truth for themselves. In other words, democracy has an epistemic function as a kind of truth machine. From this it follows that in a democracy there should be no dogma: no knowledge protected from public challenge and debate. Yet this whole argument is founded on embarrassing misconceptions of the nature of truth and of the working of democracy.