唐律乃至唐令條文中，常見到「理」，就立法意旨而言，泛言其義者多。從唐律看來，「理」實是律、令（含格、式）之外第三種具有法律效力的斷罪依據，使犯人無所逃於天地之間。其義基本上仍須由先秦典籍，尤其儒家經典去理解，間參唐以前諸儒立論，因為這是當時人的基本教養與共識。淺見以為唐律中的「理」，廣義指道理，狹義為義理。唐律本於禮，此處之禮，析而言之，具有三義：禮之儀、禮之制、禮之義；唐律中的理，大多指禮之義而言，尤其是禮所規範人際關係的義理社會價值。理不可為而為者即有罪，以此法意斷罪，影響至明清律，是傳統法制一大特質。但因「理」為抽象意義，具有不確定性，不免受到後人詬病。

The word “Reason” appeared frequently in the Tang Code or Statues. It was discussed with a wide range of meanings regarding its usage as a legal term. Seen from the Tang Code, “reason” was in fact an alternative criteria for court judgment in addition to “code” and “regulation” (including rules and forms) with legal authority. It was designed to bring the criminals to justice. This arrangement of “reason” could be understood through the pre-Qin Classics, especially the Confucian cannons, combined with the discussion of the pre-Tang Confucianists. There was a “consensus” and shared upbringings among the Tang contemporaries regarding the “reason”. My understanding of the “Reason” in the Tang Code was that it was “the Way and Truth” in general and the “righteousness” in particular. The making of the Tang Code was based on “propriety”. Here the “propriety” could be interpreted from three ways: the rituals, the institutions and the righteousness. The “reason” of the Tang Code mostly was referred to the last meaning, ie, the righteousness of the propriety. It regulated the inter-personal relationships and social values. If one committed an act which was forbidden according to the “reason”, then he was considered as a criminal and would be brought to court and sentenced. This kind of practice had influenced the making of the legal code of the Ming and Qing dynasties and was a characteristic feature of traditional Chinese legal history. However, since the “reason” is very abstractive and has no fixed definition, it has been inevitably criticized and even denounced.