C.S. Lewis discusses four categories of love in The Four Loves.
The book examines four Greek terms: affection, friendship, erotic love, and charity. Lewis uses the terms storge, philia, eros, and agape to distinguish kinds of human attachment that English often groups under the single word “love.”
The Four Loves developed from a series of radio talks and was published as a book in 1960. Lewis considers how these forms of love can enrich human life but can also become distorted when treated as absolute or self-sufficient. His discussion blends Christian theology with observations about family, friendship, romance, and charity.
The categories are analytical rather than four completely separate emotions. Lewis acknowledges overlap among them, and his treatment of agape, or self-giving divine love, gives the work its Christian framework. The book is not a sequel to The Screwtape Letters or a volume in the Narnia series.