Hume's Odd Footnote to Grotius, and Pufendorf
Readers who come to David Hume through the Treatise may be forgiven for thinking that he wasn't an especially learned or scholarly philosopher deviating from the reigning tendency toward eclecticism. I include myself among these, until I heard a paper (which may still be unpublished) by Ken Winkler on the way Hume carefully edited his notes engaged with Locke through the successive editions of the Enquiries. In fact, Hume's long essay on population exhibits him as quite learned. So much for set-up.
After offering his famous definition of convention in the third Appendix to the Second Enquiry (paragraphs 7-8), Hume adds a note suggesting that this "theory concerning the origin of property, and consequently of justice, is, in the main, the same with that hinted at and adopted by Grotius," (De jure belli & pacis. Lib. ii. cap. 2. §2. art. 4 & 5.) which he then quotes in Latin. There are four things that are peculiar about the passage from Grotius that Hume quotes.
First, throughout it his writings, Hume himself had explicitly denied that property had its origin in an explicit/verbal convention (that is, social contract), whereas Grotius explicitly allows that this is a possible source: "Simul discimus, quomodo res in proprietatem iverint; non animi actu solo, neque enim scire alii poterant, quid alii suum esse vellent, ut eo abstinerent, & idem velle plures poterant; sed pacto quodam aut expresso, ut per divisionem, aut tacito, ut per occupationem." (emphasis added.) Yes, Grotius does more than hint at his preferred account of tacit contract of property, so I am not suggesting Hume gets this wrong.
But, second, as readers of Hume would have been quite aware that's developed by Locke (and Pufendorf). In fact, I have been arguing that Hume completely effaces how much of the distinctive details his own definition of convention (including that of property) is already present in Locke (recall here; here; and see here for slightly more scholarly version).
Third the passage from Grotius cited by Hume is utterly banal. He could have cited any number of ancient authors here (from Plato's Laws to Lucretius) as one can readily see in Pufendorf's Of the Law of Nature and Nations, Book IV, chapter IV, paragraphs viii-X.
In fact, in Book IV, chapter IV, paragraph IX Of the Law of Nature and Nations, Pufendorf had partially commented the very passage from Grotius that Hume quotes. I quote Pufendorf in Basil Kennett's translation (from the fourth, corrected 1729 edition which includes Barbeyrac's notes):
Thus far Grotius is in the right, that were the first negative Communion to continue, without disturbing the general Peace, Men must live with great plainness and simplicity, contented to feed on what they found, to dwell in Caves, and either to go naked or to cover their Bodies with the Barks of Trees, and the Skins of Beasts: Whereas, if they grew more inclined to a Life of Elegance and Refinement, the Conveniences of which must be acquired by Diligence; there was a necessity of introducing distinct Properties. But when he adds, That this Communion might have lasted, had Men lived under the Influence of an eminent Charity and Friendship towards each other; he confounds negative Communion with positive; such as was observed by the Essenes of old, by the primitive Christians inhabiting Jerusalem, and by those who now follow an Ascetic Life: For this can never be constituted nor kept up, except amongst a few Persons, and those endued with singular Modesty and Goodness. When Men are scattered into different places, and fixed at a distance from each other, it would be a foolish Labour to gather all the Provision into one Heap, and to distribute it out of the common Mass. And where ever there is a great Multitude of People, many must of necessity be found, who through Injustice and Avarice, will refuse to maintain a due Equality, either in the Labour required for the getting of the Fruit, or afterwards in the Consumption of them. Plato insinuates as much as this, when he makes only Deities, and the Sons of Deities, Members of the Republic where he would have this Communion absolutely obtain. But 'tis idle to believe, that when Men were divided into numerous Families, they neither actually established, or had any design to establish such a Communion. Lastly, it's a true Remark of Grotius, That things were at first turned into Property, not by the bare Act of the Mind, or by Thought and inward inclination. For neither could others know what any Person intended to keep for his own, to direct them in abstaining from it, and besides, it was very possible that many should be Competitors for the fame thing. There was need therefore of some external Act of the Mind formal seisin [sign?],* which, that it might be capable of producing a Moral Effect, or an Obligation in others to forswear what each Man had thus taken for his peculiar, must necessarily have depended on the force of some precedent Covenant: When things which lay together in Common were to be parted amongst many, then the Business was transacted by express Covenant. But a tacit Covenant was sufficient, when Men fixed a Property in things which the first Dividers had left for waste. For we must suppose them to have agreed, that whatever in the primary Partition had not been assigned to any particular Owner, should belong to him who first took possession of it. [emphases in original; modernized spelling by ES]+
What's neat, given my present purposes, is that Pufendorf praises Grotius for exactly the passage that Hume cites as the origin of his own theory. In fact, Pufendorf's criticism of Grotius here also kind of anticipates Hume's account because Pufendorf implies that Grotius theory is too naïve: because Grotius' approach presuppose a too rosy picture of human nature ("singular Modesty and Goodness") and cannot scale up ("except amongst a few Persons"). That is, the question is, as Pufendorf shows, how can large-scale tacit social conventions be established among potentially self-regarding people? Pufendorf's own answer seems to be: through trial and error and habit/custom.
Building non-trivially on Locke (whose contribution is ignored), Hume's explicit answer is "through a sense of common interest; which sense each man feels in his own breast, which he remarks in his fellows, and which carries him, in concurrence with others, into a general plan or system of actions." This answer may seem to work if one allows, as Hume stipulates, that one generally benefits from the common interest.
However, Adam Smith recognizes that Hume's answer puts the cart before the horse, because it is not obvious how the common interest is recognized before the convention is relatively stable, and so Smith suggests that the convention itself originates in and is stabilized by drawing on our reactive attitudes (especially resentment and gratitude). But that story I have told elsewhere.
*A seisin is a possession of a fief. But it seems more likely that 'sign' is intended here in light of Pufendorf's account of the origin of social/moral entities.
+I thank Dario Perinetti for nudging me back to Pufendorf. And I thank Bart Wilson and Vernon Smith for emphasizing the importance (alongside Buckle and Haakonssen) of Pufendorf to the Scots.