Zhu Xi said in its introduction: "Most people say that love is mysterious and incredible. In fact, this introduction is wrong. This book is turned to search for the source of love, in order to investigate the signs of love evolution, special In three parts, this is the love of mother and child, the love of the opposite sex and the love of friends. ”After a systematic elaboration, Zhu Xi finally pointed out:“ The love of mother and child guarantees the development and safety of the offspring; Guarantee the reproduction of the next generation; the love of friends is the psychological basis for building a society. "These three kinds of" love ". "There are physical reasons to test, there are causal reasons to find, and they have similarities with other psychological phenomena.