《呂西斯》關於愛的哲學探討呈現了柏拉圖對於友愛和愛欲之關係的理解。在柏拉圖看來，善惡和屬己是愛的兩種截然不同的人性根據，人既可以因為惡的威脅而進行向善的努力，也可以因為對缺失的感知而追求屬己的整全。前一種追求展現了愛欲的人性邏輯，其實質是個人的縱向提升；後一種追求展現了友愛的人性邏輯，其實質是人與人的橫向聯合。本文基於對《呂西斯》主體情節與核心論證的細緻分析，試圖證明，正是上述這兩條緊密相關但是方向不同的人性線索構成了柏拉圖思考愛的根本框架。

Plato’s investigation of love in Lysis presents his understanding of the relationship between eros and philia. For Plato, “the good” and “the own” are two different grounds for love in human nature, in that human love is either for the sake of the good due to the present of the bad, or for the sake of one’s own completion due to the perception of deprivation. The former kind of love is eros which lies behind personal elevation, and the latter kind of love is philia which lies behind social association. This article offers an interpretation of the main plot and arguments of Lysis, with a view to demonstrating that the above two different grounds in human nature constitute the basic framework of Plato’s philosophy of love.