We like to think of ourselves as open-minded, reasonable and realistic. But evidence from history, psychology and philosophy suggests that we are probably deluding ourselves. Our thinking is heavily influenced by intellectual vices like closed-mindedness, overconfidence, wishful thinking, stupidity and prejudice. Philosopher Prof Quassim Cassam (University of Warwick) talks about these vices and role they’ve played in recent political events. What are they, what’s so bad about them, and what can we do to control them?