Abstract: Article 118 of the Civil Code defines the concept of obligation, but the General Part and the Specific Parts present a logical conflict between the various causes of obligation and a dilemma regarding the misalignment of the concept of quasi-contract from the perspective of extracting common factors, and this logical dilemma extends to the level of judicial practice. The dilemma arises from the different arrangements of the concept of obligation in the General Part and the Specific Parts for different types of obligation under the two-step legislative approach. From the genetic perspective, obligation originates from Roman law. In ancient Rome, the causes of obligation successively emerged in the forms of “dichotomy”, “trichotomy” and “tetrachotomy”. Up to modern times, the “pentachotomy” paradigm of the French Civil Code and the German paradigm that abandons quasi-contracts have been formed. Drawing on the legislative experience of Roman law and other jurisdictions, and from an interpretative perspective, we should apply an expansive interpretation to the “contract” in the Book on Contracts of the Civil Code as a concept that does not require mutual assent, and interpret the causes of obligation in Article 118 in accordance with the model of obligation classification in the Napoleonic Code. This can alleviate the logical dilemma of the concept of obligation. To fundamentally solve this problem, it is necessary to restructure the system of causes of obligation and incorporate the provisions on quasi-contracts into the General Part.