As tension heats up in the South China Sea, some bordering countries insist on solving the dispute simply within the framework of the United Nations Convention on the Law of the Sea (UNCLOS), but this insistence ignores history and violates inter-temporal law, a doctrine of international law.

As early as 1843, former United States secretary of state Abel P. Upshur wrote in an official letter: "A people's right to land discovered in the 16th century is determined on the basis of international law as understood at that time and not on the basis of improved upon or more enlightened views 300 years later."

Robert Y. Jennings, British scholar in international law and former president of the International Court of Justice, has said: "A juridical fact must be appreciated in light of the law contemporary with it, and not the law in force at the time when a dispute in regard to it arises or falls to be settled."

Speaking of Chinese people's discovery of Xisha and Nansha islands, Choon-Ho Park, South Korean expert in the law of the sea, expressed doubt whether modern international law is fully applicable to the historical facts of pre-modern times, saying that the discovery and use of these islands should be in line with the circumstances of that time instead of the interpretation of modern laws.

L.F.L. Oppenheim's International Law: A Treatise says: "In former times, the two conditions of possession and administration, which now make the occupation effective, were not considered necessary for the acquisition of territory through occupation". In Oppenheim's opinion, in the age of discovery, some symbolic act other than "effective occupation" was enough to justify the acquisition of territory in light of the law contemporary with it. It was not until the 18th century that international law entailed "effective occupation", and only in the 19th century did countries conform to such regulations in their practices.

Viewed in this light, inter-temporal law can play a key role in solving historical territorial disputes. China's sovereignty claim over the Xisha and Nansha islands can be justified from two aspects.

On one hand, China's sovereignty claim over the Nansha Islands can be traced back to centuries ago when there were fewer conditions for establishing title. Just as Daniel J. Dzurek, an US geographer, wrote, because the Nansha Islands and reefs were minuscule and had little economic importance until the development of extended jurisdiction under the new law of the sea, the claimants made little effort to secure clear title to them by means of occupation.