C.S. Lewis discusses four kinds of love in his 1960 book The Four Loves.
The four categories are affection, friendship, erotic love, and charity. Lewis uses the Greek terms storge, philia, eros, and agape while explaining how different forms of love can overlap, develop, or become distorted. The book grew from a series of BBC radio talks broadcast in 1958.
The categories are not presented as a simple ranking or as four completely isolated emotions. Lewis examines the strengths and dangers of each kind, including the possibility that natural loves can become possessive when separated from charity. The title refers to the four-part framework, not to four individual characters or four romantic relationships.