C.S. Lewis’s 1960 book about affection, friendship, erotic love, and charity is The Four Loves. The work develops ideas first presented in a 1958 BBC radio series and distinguishes four Greek terms used to discuss different forms of love.
Lewis examines storge, or natural affection; philia, or friendship; eros, or romantic love; and agape, which he connects with self-giving divine love and charity. He does not treat these categories as sealed compartments: human relationships can involve more than one kind of love, and natural loves can become distorted when treated as ultimate.
A frequent confusion is to identify The Four Loves as a novel or as a direct sequel to Mere Christianity. It is a work of Christian apologetics and reflection, and its radio origins connect it to Lewis’s broader public communication rather than to the Narnia fiction.