Which C.S. Lewis book discusses four kinds of love, including affection and friendship?

The Four Loves discusses affection, friendship, eros, and charity.

C.S. Lewis developed the book from a 1958 BBC radio series, and The Four Loves was published in 1960. Its central structure draws on different Greek terms and concepts associated with kinds of human love. Lewis examines storge, or affection; philia, or friendship; eros, or romantic love; and agape, which he connects with self-giving divine love.

The book does not simply rank ordinary relationships from best to worst. Lewis explores the strengths and dangers of each form, including the possibility that natural loves can become possessive or distorted when treated as ultimate.

The Four Loves is sometimes mixed up with Mere Christianity because both began as broadcast talks. Mere Christianity addressed foundational Christian belief, while The Four Loves focused on human relationships and the transformation of love.