Author and social critic Os Guinness joins us to talk about the great, and the terrible, revolutions throughout human history. Every revolutionary movement has carried the banners of Justice and Freedom. But why is it that most of them - apart from the Exodus and the American Revolution - have led to unimaginable oppression and despotism?

Os Guinness is an author and social critic. Great-great-great grandson of Arthur Guinness, the Dublin brewer, he was born in China in World War Two where his parents were medical missionaries. A witness to the climax of the Chinese revolution in 1949, he was expelled with many other foreigners in 1951 and returned to Europe where he was educated in England. Os has written or edited more than thirty books, including The Call, Time for Truth, Unspeakable, A Free People's Suicide, The Global Public Square, Last Call for Liberty, Carpe Diem Redeemed, and The Magna Carta of Humanity. His latest book is The Great Quest: Invitation to the Examined Life and a Sure Path to Meaning. Follow him on Twitter at @OsGuinness.