The Four Loves is a book by C. S. Lewis which explores the nature of love from a Christian perspective through thought-experiments and examples from literature. The content of the examination is prefaced by Lewis' admission that he initially mistook John the Apostle's words "God is Love" (1 John 4:7-9, 1 John 4:15-17) for a simple inroads to his topic. By distinguishing need-love (such as the love of a child for its mother) from gift-love (epitomized by God's love for humanity), Lewis happens upon the contemplative that the natures of even these basic categorizations of love are more complicated than they, at first, seem. As a result, he formulates the foundation of his topic ("the highest does not stand without the lowest") by exploring the nature of pleasure, and then divides love into four categories, based in part on the four Greek words for love: affection, friendship, eros, and charity. It must be noted, states Lewis, that just as Lucifer—a former archangel—perverted himself by pride and fell into depravity, so too can love— commonly held to be the arch-emotion—become corrupt by presuming itself to be what it is not ("love begins to be a demon the moment he begins to be a god").
As with other languages, it has been historically difficult to separate the meanings of these words for love. Nonetheless, the senses in which these words were generally used are given below.