The Invention of Terra Nullius
Some of the judges who took part in the case disputed the use of terra nullius. Judge Gros stated the question they had been asked to answer 'was not a legal one, that it was purely academic and served no useful purpose.' He agreed with Judge Dillard who called the question 'loaded.' Gros's words could have cooled some of the Australian enthusiasm for terra nullius:
The Advisory Opinion rightly recognizes that the concept of terra nullius was never relied upon by any of the States interested in the status of the Territory at the time of colonization; no treaty or diplomatic document has been produced relying on this concept in connection with Western Sahara, and States at the time spoke only of zones of influence. With regard to a territory in respect of which the concept makes no appearance in the practice of States, it is a sterile exercise to ask the Court to pronounce on a hypothetical situation; it is not for a court to enquire into what would have happened in 1884 if States had relied on this concept, but into what did happen.Change a few words and the date and his concerns could be transferred to the Mabo decision.
Malcolm Shaw noted Judge Dillard's observation that the topic was irrelevant and 'that Spain's original title was not in question nor had any state in fact asserted that Western Sahara was at the relevant time terra nullius.' Shaw made the observation: 'the significance of the discussion of terra nullius was that it helped establish the requisite framework for the examination of the Moroccan and Mauritanian contentions.' Similarly, the topic of terra nullius was used in Mabo to allow discussion of quite different matters. Though the Western Sahara Advisory Opinion was not the critical examination of terra nullius Brennan asserted it was, it could have provided a model for him in examining state practice at the relevant period, which in the case of the Murray Islands was 1878, not 1788.
Emerich de Vattel was referred to in Western Sahara and some of the comments involving him made their way into Mabo. Justice Brennan was elastic in his use of the eighteenth century writer, whom he used to make contradictory claims about terra nullius. He said that Vattel offered 'justification for the application of the theory of terra nullius to inhabited territory,' then nullified this by asserting that Vattel had defined terra nullius as uninhabited territory. To make that second point, Justice Brennan, and Justice Toohey, used identical words from Judge Ammoun in the Advisory Opinion: 'Vattel, who defined terra nullius as a land empty of inhabitants.'
Vattel never mentioned, never defined terra nullius. 'When he wrote of something that modern judges took for terra nullius, was it really the same thing that they had in mind when they used the term? And was Vattel defining or simply describing that elusive thing? And did Ammoun and the Australian judges both share the same meaning of terra nullius?
Vattel wrote in clear, eighteenth century French, not Latin. In The Law of Nations or the Principles of Natural Law Book 1, Chapter 18 was titled 'Occupation of Territory by a Nation,' Vattel discussed, in section 207, taking possession of 'a country uninhabited and without an owner': 'pays inhabite et sans maitre.' Our usage of terra nullius comes from the late nineteenth century and describes a condition of sovereignry. Was Vattel describing a res nullius or terra nullius? Putting together mid-eighteenth century writing and a late nineteenth century concept may not exactly mesh. Judge Ammoun was, presumably, thinking in French. He had been asked a question about 'un territoire sans maitre,' 'a territory belonging to no-one.' Was Vattel's idea of un maitre the same as his? Was Vattel thinking of sovereignty or personal ownership, or was this a later idea that really was not part of his own way of thinking? And if this really is a definition of terra nullius then it is a much, much simpler idea than that carried by the Mabo judges, and has absolutely no application to an inhabited land such as New South Wales in 1770.