 Conceptions of justice vary according to the weight they attach to each of these faces. At one extreme, some conceptions interpret justice as wholly concerned with what individuals can claim under existing laws and social conventions: thus for Hume, justice was to be understood as adherence to a set of rules that assign physical objects to individuals (such as being the first possessor of such an object) (Hume, A Treatise of Human Nature, Book III, Part II). These rules can be explained by reference to the natural associations that form in people’s minds between persons and external objects, and although the system of justice as a whole can be shown to be socially useful, there are no relevant independent standards by which its principles can be assessed (Hume briskly dismissed equality and merit as principles for allocating property to persons). In similar vein, Hayek argued that justice was a property of individual behaviour, understood as compliance with the ‘rules of just conduct’ that had evolved to enable a market economy to function effectively. For Hayek, to speak of ‘social justice’ as an ideal standard of distribution was as meaningless as to speak of a ‘moral stone’ (Hayek 1976, p. 78)