I’ve been thinking recently about three debates. In the first, which took place in January 2016, two Harvard students, Fanele Mashwama and Bo Seo, proposed that “the world’s poor would be justified in pursuing complete Marxist revolution”. In the second, in October of the same year, Hillary Clinton and Donald Trump debated which of them should be the next president of the United States. In the third, author David McRaney discussed the shape of the planet on which we live with Mark Sargent, a man best known for his popular YouTube videos asserting that the Earth is flat.

I have my own views about all three topics, but what intrigues me here is form rather than content. What does it mean to have an argument with someone? What goals are served by different styles of debate? And, most importantly of all, if you hope to persuade someone else to change their mind, how should you do it?

Mashwama and Seo were debating in a formal contest, the world championship, no less. They won, but not because they convinced anyone that a Marxist revolution was justified. (I suspect they did not even convince themselves of that.) You win a debating contest in much the same way that you win a figure-skating competition: by convincing the judges that you have produced a superlative performance, judged against established standards and rules.