Mercantile law is a lex specialis of the civil law. However, mercantile law does not completely fulfill the legal demand for commercial transactions, and is applied with civil law. Therefore, the statement that mercantile law is a special type of civil law should be recognized in such a way that an article in civil law, in correspondence to an article of mercantile law, should follow the article in mercantile law.
If an institution of civil law repeats itself in specific institution of mercantile law and its subjects, the only way to integrate the two based on civil law that applies to basic law is to start from the results of legal research of mercantile institution. On the contrary, the casual approach which starts from legal theories denies the peculiar and independent characteristics of mercantile law and is seen as an approach that does not fully consider the peculiarities of the law from reality. However, it is noticeable that especially field of commercial activities and commercial general provisions that accentuates their relation to civil law is in a blind spot, far from the area of main interest for mercantile law.
The prerequisite requirements for the integration of civil law and mercantile law in way of legal theories, and not simply the integration of the two, have to be approved by the legal sources and the aspects of mercantile law. If not approved, the integration would not be plausible. Art. 1 Commercial Code for the existing forms of law for commercial transactions states, 「if the original law by business affairs does not have regulations, rely on mercantile law and if there is no mercantile law, follow regulations of civil law」. Studies of mercantile law often analyze that mercantile law is based on general principles od civil law, but they also state that the field in which civil law applies is different from the field in which mercantile applies, and therefore agree that civil law does not equal the area in which mercantile law can be applied to. As a result, it is said, Art. 1 Commercial Code is no more than the regulation of applied law of order that relate to business affairs. Nonetheless, nowadays, the definition on merchants and commercial activities does not only completely lack the skill, but they also we can conclude that civil law lacks the characteristics of special relation laws from the fact that the function of civil law as a basic law has been disregarded. Thus, from the perspective of the legal sources, the basic for the integration of civil law and mercantile law has already been established. On the other hand, the attitude of trying to approving general terms and conditions and commercial autonome rules that apply to the interpretation of business affairs as a part of law is improper, because in order to be approved, they should have to have solid foundation in (real-world) law.
Next, the distinction between customary mercantile law and (real-world) mercantile law is unclear. The distinction is unclear especially between customary mercantile law and factual mercantile custom, but considering that the supreme court established that customary mercantile law is a law with an effect to fulfill which exists objectiv, the dibate about a customary mercantile law is now exhaustive. From an aspect, the fact that that customary mercantile law and true customs are approved by the court’s trial activities is not any different from any others. Furthermore, we cannot deny that commercial transactional practices play a big role in trial activities, unlike civil law, but we must keep in mind that this is only in theory.
Finally, the codification of laws enacted is centered on ideas of reform, integration and rationalization, and such philosophy is achieved through legal amendments. The integration of civil law and mercantile law should also free itself of existing legal conflicts and contradictions that are caused by different fields in which the two apply, and start from reasonably elaborating the theories. Surely, in case of considering a new code there shall be no need to comprehend the two laws, because the theoretical conflicts that concern the court can be eliminated by the method of legislation.
In any situation, it is hard for any integration where the principles of mercantile law is not arranged clearly to have any value. If the principles of mercantile law are not straightened, the special existing form of law court can make the integration meaningless by accentuating the peculiarities of mercantile law. For that reason, cooperation of the scholars of mercantile law and civil law for integration of the two laws is clearly an urgent issue.