The C.S. Lewis book that presents four forms of love using Greek terms such as storge and agape is The Four Loves.
The book developed from a series of BBC radio talks broadcast in 1958 and was published in book form in 1960. Lewis examines affection, friendship, erotic love, and charity, using Greek vocabulary to distinguish kinds of love that English often treats with one broad word.
The four terms discussed are storge, or affection; philia, or friendship; eros, or romantic love; and agape, which Lewis associates with charity or self-giving love. The book does not claim that real relationships always fit into only one category. Instead, it explores how these forms of love overlap, develop, and sometimes become distorted.
The Four Loves is distinct from Mere Christianity, which grew out of earlier wartime broadcasts, and from The Problem of Pain, another major apologetic work. Lewis’s treatment combines Christian theology with observations about family, friendship, desire, and human dependence, making it one of his most accessible nonfiction books.