China, Philippines send ships to disputed island. What if they sent lawyers?

Both China and the Philippines have legal grounds for its claim on the Scarborough Shoal in the South China Sea. Here's how the arguments shape up.

The Philippines and China are holding their ground in a tense dispute over Scarborough Shoal in the South China Sea, as the Chinese sent a third ship to the region today and the Philippines sent a coast guard ship to replace their flagship as it refueled. But a peaceful resolution to the impasse is still being sought.

One of the ways out may be taking the dispute to an international tribunal or the International Court of Justice. But international law may not be able to provide an obvious resolution, as each side has grounds for its claim on the island.

Philippines officials have said that their case under international law would be based on the 2002 Declaration on the Conduct of Parties in the South China Sea. Both China and the Philippines are signatories to the Convention, which is a treaty between the Association of Southeast Asian Nations (ASEAN) and China that states how disputes in the South China Sea will be dealt with. The key clause here is the fourth, which reads:

4. The Parties concerned undertake to resolve their territorial and jurisdictional disputes by peaceful means, without resorting to the threat or use of force, through friendly consultations and negotiations by sovereign states directly concerned, in accordance with universally recognized principles of international law, including the 1982 UN Convention on the Law of the Sea;

The 1982 UN Convention on the Law of the Sea, in turn, sets out international laws on nations' claims to resources located off their shores. The Convention divides offshore regions into zones, with each zone permitting a different amount of access. In the Scarborough Shoal dispute, the region at issue is the "Exclusive Economic Zone," or "EEZ," the area up to 200 miles off the coast of each nation wherein that nation has sole right to exploit the natural resources located in the ocean and on the ocean floor. Such resources can include fish, natural gas, and oil.

Besides being signatories of the Declaration, both China and the Philippines also signed and ratified the Convention, theoretically incorporating the treaty's provisions into their national laws. 

The Scarborough Shoal is located less than 150 miles off the Philippine coast, and more than 500 miles away from the Chinese coast. Thus, Manila would argue that the Shoal is well inside their EEZ – and far, far from the Chinese EEZ – giving the Philippines sole claim to its resources and sovereignty over the region.

The Chinese claim is less clear cut, as it is based on historical claims, but still has teeth under international law. International law largely developed out of the customs that nations used when interacting with each other. As such, a nation that is able to show that it has long controlled a region or a resource can argue that it has established a rightful claim. 

It is such thinking that drives China's claim. As Chinese state news agency Xinhua writes, the Chinese embassy in the Philippines argues that Chinese fisherman have long plied their trade around the Scarborough Shoal, which the Chinese call Huangyan Island. Xinhua writes that China has "abundant historical and jurisprudence backings" for its claim, and the embassy argues that "The fact that China has sovereign rights and exercises jurisdiction over the Huangyan Island is widely respected by the international community." Thus, they say, sufficient custom exists under international law to establish China's claim.

Further, China specifically claimed "sovereignty over all its archipelagos and islands" recognized under Chinese law, even as the government ratified the Convention in 1996. This allowed the Chinese to keep their claim to the Scarborough Shoal and other islands in the South China Sea and elsewhere, even as they agreed to the other terms of the treaty. As such, they can argue against the Philippines' invocation of the Convention, even though the Convention is recognized by China.

Ultimately, international law is both malleable and slow-acting, so factors like military might or soft economic power may resolve the impasse before an adjudicated solution can be found. But should the international law solution come to a head, it is unclear which nation, China or the Philippines, would prevail.