We question the basis of July's ruling by an international tribunal that the disputed Spratly Islands (Nan-sha Islands) in the South China Sea are merely rocks (see Nature 535, 334–335; 2016).

According to the United Nations Convention on the Law of the Sea, which is signed by 178 countries, an island is defined by three elements: it is a natural formation; it lies in the same territory and economic zone as the surrounding sea; and it can sustain human habitation or have an economic life of its own (see go.nature.com/2bj4sit).

One of the disputed islands, Taiping Island, fulfils all three criteria, having its own freshwater resources (see go.nature.com/2biujnv; in Chinese). There is also human habitation and economic activity on several of the other islands.

In our view, the international court seems to have interpreted an island's third defining element as requiring no external resources to sustain human settlement. If that were the case, the Maldives, Singapore and Hong Kong should probably be considered as rocks — they bring in gas and must obtain much of their fresh water by import and desalinization or from rain water.