Melvyn Bragg discusses the life, works and enduring influence of the medieval philosopher and theologian St Thomas Aquinas with Martin Palmer, John Haldane and Annabel Brett. St Thomas Aquinas' ideas remain at the heart of the official doctrine of the Roman Catholic Church today and inform philosophical debates on human rights, natural law and what constitutes a 'just war'.Martin Palmer is Director of the International Consultancy on Religion, Education and Culture; John Haldane is Professor of Philosophy at the University of St Andrews; Annabel Brett is Lecturer in History at Gonville and Caius College, Cambridge.