本文藉著比較情詩與淫詩，試圖找出朱子判定「淫詩」的標準。關於朱子淫詩的標準，已有學者指出一二，本文進一步列出朱子所謂「淫詩」，並加以分析，具體歸納朱子的淫詩標準。發現情詩不等同淫詩，主要的區別關鍵是，朱子認為要得「性情之正」。因此本文要繼續追探情感的正與偏之分際為何？ 《詩集傳》中情詩的愛情主角多半以男性為主體，如〈關雎〉〈漢廣〉，詩中的未婚女性都扮演儼然不可犯的角色。情詩中已婚女性，多具有溫柔賢淑的傳統婦德。而違反社會的倫理規範之愛情為「淫」。例如：（1）、在婚姻以外之感情。（2）凡是男女不經父母之命，媒妁之言的嫁娶，而私相自由戀愛就是淫；《詩經》中所有男女在婚前的戀愛詩，朱子都斷為淫詩。因此我們不禁要進一步追問，是社會規範成為天理（道德原則）的判準？社會規範與天理（道德原則）之間的關係為何？並檢討理學代表人物朱子對天理的認定標準。

This paper compares affection poems and lust poems and attempts to find out Chu-tzu’s standard in discriminating between these two types of poems. Chu-tzu first proposed some poems may be called lust poems. He highly regarded the collection of love songs of ordinary people in the 《Book of Odes》, thus negating the view expressed in the 《Prologue of the Collection of Poetry》that poems in the Book of Odes are mostly praise and sarcasm. Poems that express mutual affection between men and women need not always be lust poems. According to Chu-tzu, the main dividing line is this: Affection poems express “pure” affection and love whereas lust poems express “defiled” love and affection. The question then is: how to distinguish between these two kinds of love? The main characters of love poems are mostly men. This feature can be found in some famous love poems 〈Kwan-Ju〉, 〈Han-Kang〉. Unmarried women in those poems usually possess high moral integrity that cannot be trespassed. Married women in those poems possess gentle integrity and traditional ethics. Love that violates established social fabrics governing interpersonal relationships is deemed as “lust”. This includes: (1) love and affection outside marriage, (2) marriage not endorsed by parents and arranged by marriage brokers but through the free will of the couple is deemed as “lust”. Chu-tzu regarded all poems that described affection before marriage as lust poems. Consequently we have to ask: are social fabrics the only yardstick of heavenly theory (moral principle)? What is the relationship between heavenly theory (moral principle) and social fabrics? We also discuss rationalism as the standard Chu-tzu used to lay down his heavenly theory.