C.S. Lewis discusses four types of love in The Four Loves.
The book examines four Greek terms: storge, affection or familial love; philia, friendship; eros, romantic or sexual love; and agape, selfless or charitable love. Lewis explains that these categories overlap, but each highlights a different way people relate to one another.
The Four Loves developed from a series of BBC radio talks and was published as a book in 1960. Lewis combines literary examples, philosophical reflection, and Christian theology rather than presenting a scientific classification of emotions.
A common mix-up is to treat agape as the only kind of love Lewis considers important. Instead, the book explores all four and asks how human loves can be strengthened, distorted, or understood in relation to divine love.