Which C.S. Lewis work presents a fictional debate between a senior demon and a younger demon about human temptation?

The C.S. Lewis work presenting a fictional debate through demonic correspondence is The Screwtape Letters.

The 1942 book consists of letters written by Screwtape, an experienced demon, to Wormwood, his inexperienced nephew and trainee. Rather than presenting temptation from a human or angelic viewpoint, Lewis reverses the perspective and makes the demons explain how they hope to mislead a person.

The letters discuss ordinary situations such as irritation, vanity, social pressure, romantic attachment, and religious distraction. Their force comes from the gap between the demons’ goals and the moral conclusions readers are meant to draw. Screwtape’s confident advice frequently reveals the absurdity and destructiveness of the demonic system.

Although the book is fictional, it is not usually classified as a novel in the same way as Lewis’s space fiction or Narnian stories. It is an epistolary apologetic work. Lewis’s later “Screwtape Proposes a Toast” extends the concept but is not the title of the original correspondence.