IT IS hard to have an argument with only one person in the room, but the Philippines is having a go. On July 13th a tribunal in The Hague concluded a first week of hearings related to its bitter dispute with China over maritime boundaries in the South China Sea. China insists that its claim, which covers most of the vast and strategically vital sea, is not a matter for foreign judges, and was not represented. Such has been China’s position ever since the Philippines lodged a case in 2013 at the Permanent Court of Arbitration in The Hague, arguing that the U-shaped, nine-dashed line used by China to define its claim is illegal. But in its anxiety to dismiss the validity of the case, China may have blundered. The tribunal has ruled that documents issued by China to explain its objections “constitute, in effect, a plea”. The tribunal has sent all the relevant papers to the Chinese government and given it time to respond. China has become a participant in the case, despite its absence.

The most significant document noted by the tribunal is a lengthy “Position Paper” published by China’s foreign ministry last December. This repeated China’s frequent assertion that it has “indisputable sovereignty” over the islands of the South China Sea and “adjacent waters”. Chinese officials did not formally submit the paper, which would have risked implying acceptance of its arbitration. But the tribunal is considering it anyway.

The tribunal will not rule on ownership of the dozens of reefs and islands in the South China Sea and the waters around them. Instead, its ruling is sought on whether features in the sea that are claimed by China could be used as a basis for the claims it makes. The United Nations Convention on the Law of the Sea (UNCLOS) sets out how different maritime features generate claims to territorial waters and “exclusive economic zones” (EEZ). A reef submerged at high tide generates nothing, while a rock above water has a 12- nautical-mile (22km) territorial claim around it. A habitable island generates an additional EEZ of up to 200 nautical miles from its shore.

The Philippines argues that none of the features China occupies in the Spratly Islands is an island. At best, it says, each is entitled only to a 12-nautical-mile claim and none generates an EEZ. For almost the past two years China has been frantically reclaiming land around these features and expanding their size, adding buildings and, in some cases, new airstrips and harbours. But UNCLOS is clear: man-made structures do not count.

The Philippines hopes that if the tribunal accepts its argument, then China’s U-shaped line would look even more far-fetched than it does already. China would at best be able to claim a few small circles drawn around a few tiny features. Other claimants, including the Philippines, which also have claims to some or all of these features, would continue to dispute even these little dots.

The tribunal must first decide whether it has the jurisdiction to hear the case at all. If it concludes that it does, which may not be known until late this year, a verdict may take several more months. If the Philippines wins, China will almost certainly refuse to accept the decision. Even the hope that a moral defeat would have a chastening effect on China’s behaviour seems a little tenuous, given the gusto with which it is filling in the sea.