This essay presents in short form the main argument in Three Pictures of Contract: Power, Duty and Compound Rule, 83 N.Y.U. L. Rev. (forthcoming 2008), available at SSRN: http://ssrn.com/abstract=1033116. The essay will appear in the online publication, The Legal Workshop.The article argues that contract law is unusual in that it is at one and the same time both, in Hart's terms, a duty-imposing and power-conferring rule. While most laws are of either one type or the other, an analysis of contract law shows how a single set of legal rules can be designed to both impose duties on persons and grant them the power to change their legal obligations. The analysis casts new light on contract law, supporting pluralist theories of the practice. It also adds to the general theory of normative powers, as it describes a new distinction between pure power-conferring rules and what I call "compound rules" like the law of contract.