The power of song: Laurie Taylor talks to James Walvin, Professor of History Emeritus at the University of York and author of a new study which explores the cultural history of "Amazing Grace," one of the transatlantic world's most popular hymns and a powerful anthem for humanity. How did a simple Christian hymn, written in a remote English vicarage in 1772, come to hold such sway over millions in all corners of the modern world? Also, Angela Impey Professor of Enthomusicology at SOAS, argues that songs in South Sudan can be key platform for truth-telling, often invested with greater moral force than other forms of communication in the context of 50 years of civil war. What role can songs play in the struggle for peace and justice? Producer: Jayne Egerton