《民法典》第552条将债务加入作为债法的一般规则而新设，补充了债务转移的制度体系。如何从解释论的角度，围绕《民法典》以及相关规范厘清债务加入认定中的诸多问题对于解决司法裁判中的难题具有重要意义。债务加入在我国民法语境下必须同时具备两个法律关系才能够发生：原债关系和债务加入关系。《民法典》允许四种达成“加入债务”的合意的方式，分别可以由第三人或债务人向债权人发起，债权人在合理期限内不明确对“加入债务”的意思表示作出拒绝或者直接参与订立而达成。债权人在获知第三人“加入债务”意思表示时合意达成。另外，债务人同意不是合意达成的必要条件。区分债务加入与其他相似制度的核心在于对案件事实中第三人真实意思表示的确定。债务加入与保证最显著的差异是责任承担顺位的补充性。区分债务加入和保证的关键是“第三人在同一性原则下承担连带债务”。在此前提下，辨识债务加入与保证的步骤：首先，考察系争承诺文件中的具体措辞。其次，运用“第三人在同一性原则下承担连带债务”这一债务加入的特征进行判断。如果从第三人意思表示中，得出债权人无法请求第三人或债务人或者全部债务人履行全部债务的解释，则可以直接排除债务加入，争议事实可能为其他担保制度；如果第三人在此方式下承担债务，再额外约定履行期限、履行场所、附停止条件等则可以认定为债务加入；如果第三人在此方式下承担债务，再额外约定第三人与债务人之间所应承担的份额大小、或是约定关于追偿的问题，可以将该约定视为独立于债务加入合同的内部约定。再次，考量各种因素适用利益标准进行判断。最后，意思表示仍然存疑时推定为保证。区分债务加入与第三人履行制度的关键是“第三人取得原债的债务人地位”。具体而言：辨识债务加入与免责的债务承担可以“债务人不退出原债关系”为主要标准、“债权人同意”为次要标准进行考察。辨识债务加入与第三人代为履行、利益第三人合同可围绕“第三人成为原债关系的债务人”进行考察。

Article 552 is a new article of the Civil Code, which supplements addition of new debtor to the general rules for the transfer of debts. From the interpretation perspective, it is essential to clarify the issues in recognition of addition of new debtor in the Civil Code and related legislation to solve the difficulties in judicial decisions. In the context of the Civil Code, addition of new debtor can only happen if there are two legal relations at the same time: original debt relationship and debtor adding relationship. The Civil Code allows four ways to reach the agreement of "adding new debtor". It can be initiated either by an agreement between a third party and the debtor with notification to the creditor, or by the third party expressing directly to the creditor his/her willingness to be added as a debtor. If the creditor does not expressly make a refusal within a reasonable period of time, or the creditor directly participated in the agreement, then the debtor adding contract is effectively established. The agreement is reached when the creditor is informed that the third party is willing to join. The debtor's consent is not a necessary condition for agreement. The essential point of distinguishing addition of new debtor from other similar types is to recognize the real intention of the third party in specific case. The most significant difference between addition of new debtor and guarantee is the complementary order of undertaking liabilities. In other words, "the third party undertakes solidary obligation". In this regard, the steps to identify addition of new debtor and guarantee are as follows: Firstly, check specific wording in commitment document. Secondly, judge by the nature that the third party undertakes solidary obligation under the principle of identity. If the third party's interpretation makes it impossible for the creditor to request the third party/ the debtor/ all the debtors to perform, the fact may be other guarantee types rather than addition of new debtor; If the third party undertakes the debt in such a manner, and additionally agrees on the performance period, performance venue and suspension conditions, etc., it may be deemed as addition of new debtor; If the third party undertakes the obligations, and additionally agrees clauses such as the size of share or the issue of recovery, such clauses may be regarded as an internal agreement independent of the debtor adding contract. Thirdly, considerate various factors and make a judgment by applying interest criteria. Finally, if the expression of intention is still doubtful, it shall be presumed as guarantee. The key to distinguish addition of new debtor from the complete substitution of new debtor, is to check whether “the third party obtains the original debtor's status”. In practice, we should judge by the feature that "the debtor does not withdraw from the original debt relationship", supplemented by "the creditor's consent". Distinguish and analyze addition of new debtor and the third party performing or the contract of benefiting the third party can be investigated by focusing on the point that "the third party becomes a debtor of the original debt relationship". Distinguishing addition of new debtor from the guarantee can firstly be carried out by examining the specific wording of the text using three types of methods. Secondly, the elements and characteristics of the debtor adding contract can be used to exclude situations that do not meet the requirements of addition of new debtor. The interpretation standard of "direct practical benefit to the third party himself" should be comprehensively applied. Lastly, when the third party's intention cannot be determined, the presumption rules should be adopted, and the act in question is deemed as guarantee.