Mere Christianity is a Christian apologetical book by the British author C. S. Lewis. It was adapted from a series of BBC radio talks made between 1941 and 1944, originally published as three separate volumes: Broadcast Talks (1942), Christian Behaviour (1943), and Beyond Personality (1944). The book consists of four parts: the first presents Lewis's arguments for the existence of God; the second contains his defence of Christian theology, including his notable "Liar, lunatic, or Lord" trilemma; the third has him exploring Christian ethics, among which are cardinal and theological virtues; in the final, he writes on the Christian conception of God.