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In the “two-plus-two” meeting that took place last week, the Japanese and U.S. governments unequivocally called out China, highlighting the country’s unilateral and unlawful attempts to change the status quo in the Indo-Pacific. Since then, there has been much debate on what this means for the region, especially in the context of Taiwan.

Hypothetically, imagine an incident occurs between China and Taiwan that kicks off an escalation cycle, and China decides to exploit the opportunity to realize its long-standing desire to take over the island nation. How does Japan respond in that situation?

The specific issue of what Japan will do is a policy question to which there is no definitive answer. After all, policies change and it is difficult enough to predict what will happen in the politics of the day, let alone of the future. However, there is the question of what Japan can do. In other words, what is allowable under international law and Japan’s domestic legislation?

The answer to the international law question is quite simple, as it is codified in the U.N. Charter and clarified under substantial legal precedent from International Court of Justice rulings. In short, under international law, Japan would be able to use military force in the exercise of collective self defense, provided the Taiwan government requested it.

Things get a little murkier when one starts looking at Japan’s domestic laws. Many are aware of Article 9 of Japan’s Constitution, which prohibits the use of military force as a means to settle international disputes. Under a black-and-white interpretation, this may suggest that Japan could not exercise collective self-defense and therefore would not be able to do much in support of Taiwan.

Most observers of Japanese security will know that almost nothing in Japanese security practice is black-and-white, least of all the interpretation of Article 9 of the Constitution. The Constitution, although never amended, has been reinterpreted a couple of times. The most recent reinterpretation occurred in July 2014 to clarify that Japan is in fact able to exercise collective self-defense in a limited way.

This interpretation was formally codified into law in the 2015 Peace and Security Legislation. While legal scholars could go on and on about all the different aspects of the 2015 bills and their implications, the most important thing to understand about them is that they established three specific situations. Cabinet and Diet-level declarations of those situations open up menus of authorities for the Japanese government and the Self-Defense Forces.

The first situation is the kokusai heiwa kyodo taisho jitai, or, as the Japanese government translates it, the situations where the international community is collectively addressing peace and security (for ease of reference, let’s call it the “coalition response situation”).

The Coalition Response Situation was envisioned for something like a crisis in the Strait of Hormuz. Japan’s available mission sets for this type of situation are limited to logistics support, search and rescue, and ship inspection operations, and under no circumstances are SDF personnel authorized to participate in combat operations. Many of the legal principles under Coalition Response Situations build upon Japan’s Special Measures Laws passed shortly after 9/11 to enable SDF support to the U.S. Global War on Terror. Therefore, this situation, which involves looser ties to Japan’s individual self defense, is unlikely to cover the Taiwan scenario posited above.

The second type of situation is the jyuyo eikyo jitai, or important influence situation. This is where a security crisis emerges that, if gone unchecked, has the potential to affect Japan’s own security. The Important Influence Situation is an evolution of what was previously called “Situations in areas surrounding Japan,” meaning the Japanese government really envisions this for regional scenarios that involve North Korea or Taiwan.

Under an Important Influence Situation, Japan would not have the authority to participate in combat operations; rather, it would be able to provide similar support as codified under the Coalition Response Situation (logistics support, search and rescue, and ship inspection operations). There are a few additional things that Japan could do in this circumstance, such as minesweeping, protection of military and civilian craft as they enter and exit the combat theater, and provision of facilities on Japanese territory to support partner governments and militaries actively engaged in the security crisis.

The final situation is the sonritsu kiki jitai (survival threatening situation”), in which a country that is a close partner of Japan falls under attack, and Japan’s own survival is at stake. In a China-Taiwan clash, this could be the situation at hand if Taiwan requested Japan to exercise collective self-defense, or if the United States were involved and requested the same. Under a Survival Threatening Situation, almost all the authorities are made available that the Japanese government and SDF would have if Japan itself were under attack.

However, there’s a big catch. The restrictions under declaration of a Survival Threatening Situation are so strict, it is questionable whether such a situation is actually declarable or if there would even be any utility in pursuing it. Japan can only declare a Survival Threatening Situation and exercise collective self-defense under three conditions: First, the government must credibly demonstrate that Japan’s own survival is under threat; second, it must determine that there are no other means available to resolve the situation; and third, whatever force it uses must be to the minimum extent possible.

To ensure it meets those three conditions, the law codifies that the Japanese government must build a basic plan (kihon keikaku) that clearly lays out everything the SDF and other government authorities will do in response to the situation from start to finish. This essentially establishes a positive list of authorized activities, meaning that only the things included in the basic plan will eventually be executable. That basic plan must then make it through a cabinet decision before going to the Diet for approval. Only then can the Japanese government exercise authorities made available under the Survival Threatening Situation.

Understanding all these legal conditions, it becomes quite apparent what Japan’s response could be in a militarized conflict between China and Taiwan. Japan would likely pursue declaration of an Important Influence Situation, in which case the SDF would be looking at conducting support activities outside of combat operations, while the Japanese government provides facilities and bases from which partner militaries could employ in support of the defense of Taiwan.

Of course, this is just what the law specifically lays out, but when push comes to shove, it will all come down to what Taiwan needs in a specific scenario and the policy decisions the Japanese government is willing to make. Will Taiwan request Japan to exercise collective self defense? Will the Japanese government decide to declare an Important Influence Situation or a Survival Threatening Situation, or will they just shoot straight past those and pursue a Special Measures Law? How will Japan employ its top tier diplomatic and economic power to leverage outcomes in this situation instead of trying to use the SDF?

There are many more unanswered questions out there than what this article can address. Still, understanding what the law says Japan can do and the legal process for doing it provides realistic expectations. For anyone now looking at the problem set of China and Taiwan, realistic expectations help make better policy.

Michael MacArthur Bosack is the special adviser for government relations at the Yokosuka Council on Asia-Pacific Studies. He previously served in the Japanese government as a Mansfield fellow.

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