Professor Liam B Murphy, Herbert Peterfreund Professor of Law and Philosophy at New York University School of Law gives the 2013 Annual Lecture in Law and Society. In the wake of the House of Commons Debate on tax fairness and increasing public outrage at tax avoidance by Google and other multinationals, Professor Murphy will assess how misunderstandings of the ethical bases of the central legal institutions of a market economy badly distorts political debate on tax and other issues of social justice. Unlike some other parts of the law, the law of property and contract cannot plausibly be understood as attempts to enforce moral rights and duties that legal subjects have naturally, independently of law. They must be understood as Hume understood them: The legal rules of property and contract are artificial, or conventional, in that their justification lies in their effects on overall social welfare and justice. Once the law of property and contract are established, however, it is hard not to think of them as directly reflecting real rights and duties. The law of the market encourages a kind of everyday libertarianism in social attitudes. This illusion leads us to believe, for example, that pre-tax income and wealth represent moral entitlements that should be used as a baseline in discussions of tax justice. The common criteria of tax fairness - vertical and horizontal equity - demand that those with more pre-tax income pay proportionately more tax, and that those with the same pre-tax income pay the same. But justice is not a matter of applying some equitable-seeming functions to a morally arbitrary initial distribution. The social illusion generated by the law of the market also distorts political discussion of contract. Everyday libertarianism lies behind the idea of freedom of contract. More surprising, it misleads some economic analysts of law, who would be the first to insist on the conventional nature of the law of contract.