This article was written to examine the validity of the Supreme Court ruling 2019da246016 issued on September 21, 2023(unpublished), in which the main issue was the criteria of determining whether additional terms in a contract stipulate contractual conditions (the contract takes effect if the party meets the conditions by performing its obligation), or an unfixed period (the contract takes effect if the party performs its obligation within an unfixed period). For this purpose, the research was conducted in this article in the following sequence. The academic theories and precedents were analyzed and organized regarding contractual conditions and an unfixed time limit under the Civil Act, as well as the basis of determining whether additional contractual terms represent contractual conditions, or an unfixed period within which the obligation must be performed. Based on this analysis, the reasonableness of the Supreme Court's ruling 2019da246016 issued on September 21, 2023(unpublished) was reviewed, which held that the language of the additional contractual terms stipulates an unfixed period. As a result, it has been determined in this article that the Supreme Court ruling 2019da246016 issued on September 21, 2023(unpublished) is reasonable based on the following points: In a bilateral contract for consideration, such as a sale contract, or a sub-contract, if the nature of the contract of the price payment, or the performance of the initial obligation is contested, in light of the nature of the bilateral contract with consideration, it should generally be interpreted that the contract prescribes an indefinite period, in principle; even based on the language of the contract, it is difficult to believe that it is the intent of the parties that the defendant may delay performing the obligation of making the balance payment forever unless the plaintiff fully performs the obligation of returning the membership deposit; even if various circumstances are considered which support the fact that the plaintiff and the defendant did not make the obligation of fully returning the member deposit a condition for the balance payment in the sales contract, it should be regarded that the time limit is unfixed for the return of the membership payment; from the perspective of equity, or specific reasonableness, for a party to have the obligation of making the sales balance payment, the other party shall return of the membership deposit by an unfixed time limit.
 The Supreme Court ruling 2019da246016 issued on September 21, 2023(unpublished) was based on the basic legal principle in the previous court decisions regarding the criteria of distinguishing between contractual conditions and an unfixed period, and will serve as another precedent worth referring to in similar cases in the future, for differentiating between contractual conditions and an unfixed period. Although the exercise of distinguishing between contractual conditions and an unfixed period is basically a question of interpreting a legal act, it is also instrumental in typifying the criteria for distinguishing between the two based on actual cases which build on the Supreme Court decision 2019da246016 on September 21, 2023(unpublished). It is hoped that the criteria distinguishing between contractual conditions and an unfixed period within which the obligation should be performed will be presented in more detail through additional discussions and the accumulation of more court decisions.