united to Spain), and, probably at the request of the directors of the East India Company, Grotius then detached the part of his work which dealt with the freedom of commerce and navigation and published it in March 1609, under the title of _Mare Liberum_. In dealing with his theme Grotius attacked in succession all the arguments put forward by the Portuguese to justify their claim. Their titles from prior discovery of the Cape route, under Papal Bulls, by the right of war or conquest, or from occupancy and prescription, were all, he maintained, invalid; by the Law of Nations navigation and commerce were free to all mankind. The action of the Portuguese in attempting to restrain the trade with India furnished a just cause of war; and the Dutch were resolved to assert their rights by force. But _Mare Liberum_ was much more than a pleading in a particular case. An earnest and powerful appeal was made to the civilised world for complete freedom of the high seas for the innocent use and mutual benefit of all. Grotius spoke in the name of humanity as against the selfish interests of a few; and while he made full use of arguments founded on Roman law, on the law of nature and of nations, it was principally the lofty moral ideas which inspired his work that gave it its reputation and charm. He entered into a subtle and learned disquisition as to the origin of the idea of property from the primitive times when all things were held in common; the conditions under which private property is possible or lawful, and the distinction between what is private, what is public, and what is common. Much of the argument appears to us now to be of the nature of hair-splitting and word-play; but inasmuch as it was made use of subsequently in the numerous controversies regarding the freedom or the sovereignty of the sea, as well as in diplomatic negotiations, it is necessary to summarise it here. All property, he says, is based upon possession or occupation (_occupatio_), which requires that all movable things shall be seized and all immovable things enclosed; things that can neither be seized nor enclosed cannot become property: they are common to all, and their use pertains not to any particular people but to the whole human race. The distinction is also made between things which are exhausted by promiscuous use and those which are not: the latter are common, and their free use belongs to all men. Thus the air is common, because it cannot be occupied and because it cannot be exhausted by promiscuous use; it therefore belongs to all mankind. And in the same way the sea is common to all; it is clearly so infinite that it is not capable of being possessed, and is fitted for the use of all both for navigation and fishing.[619] It is also among those things which cannot be bought and sold--that is, which cannot be lawfully acquired; whence it is, strictly speaking, impossible to look upon any part of it as belonging to the territory of a people.