C.S. Lewis discusses philia, the Greek-derived word for friendship, in The Four Loves.
The book, published in 1960, examines four kinds of human love using Greek terms: affection, friendship, eros, and charity. Lewis uses philia for the love of friendship, especially the bond formed by shared interests, activities, or a common outlook.
Lewis distinguishes friendship from companionship. Companionship may arise simply because people share a task, while friendship involves recognition that another person shares a significant interest or vision. He presents friendship as a valuable form of love, even though it is often treated as less important than romance.
The terms can be confused because Lewis’s English labels and Greek vocabulary do not map perfectly onto modern categories. In particular, charity corresponds to agape in the book’s framework, while eros refers specifically to romantic or sexual love.