 The law of contracts, at least in its orthodox expression, concerns voluntary, or chosen, legal obligations. When Brody accepts Susan’s offer to sell him a canoe for a set price, the parties’ choices alter their legal rights and duties. Their success at changing the legal landscape depends on a background system of rules that specify when and how contractual acts have legal effects, rules that give the offer and acceptance of a bargain-exchange a central role in generating obligations. Contract law conceived as a body of rules empowering individuals to shape their own rights and responsibilities presents an object of philosophical study.