This lecture examines the Preface to the encyclical. It sets forth the claims (1) that much of secular ethics finds no objective or absolute truths of morality and (2) that Catholic moral theology makes a sound case for holding that objective and absolute moral truths can be known both by revelation and by philosophical reasoning about human nature.  This lecture also provides an introduction to such terms as “human nature,” “human person,” and “natural law ethics.”

catholicthinkers.org

https://youtu.be/RnFww93qdBU