  Hume argues that we create the rules of ownership of property originally in order to satisfy our avidity for possessions for ourselves and our loved ones, by linking material goods more securely to particular individuals so as to avoid conflict. Within small groups of cooperators, individuals signal to one another a willingness to conform to a simple rule: to refrain from the material goods others come to possess by labor or good fortune, provided those others will observe the same restraint toward them. (This rule will in time require more detail: specific rules determining who may enjoy which goods initially and how goods may be transferred.) This signalling is not a promise (which cannot occur without another, similar convention), but an expression of conditional intention. The usefulness of such a custom is so obvious that others will soon catch on and express a similar intention, and the rest will fall in line. The convention develops tacitly, as do conventions of language and money. When an individual within such a small society violates this rule, the others are aware of it and exclude the offender from their cooperative activities. Once the convention is in place, justice (of this sort) is defined as conformity with the convention, injustice as violation of it; indeed, the convention defines property rights, ownership, financial obligation, theft, and related concepts, which had no application before the convention was introduced. So useful and obvious is this invention that human beings would not live for long in isolated family groups or in fluctuating larger groups with unstable possession of goods; their ingenuity would quickly enable them to invent property, so as to reap the substantial economic benefits of cooperation in larger groups in which there would be reliable possession of the product, and they would thus better satisfy their powerful natural greed by regulating it with rules of justice.