One of the major unmarked developments in the past century of American law has been the decline of natural law thinking. Read any older treatment of, for example, property rights, marriage, or contract, and the unquestioned approach looks to natural law principles to set out the basic parameters of these social arrangements. Individuals by nature had the right to own and acquire property, and that gave them the full right to the exclusive possession, use, and disposition of their things. Marriage was a union between a man and woman to carry out nature’s purpose of reproduction. Contract was the body of rules that allowed individuals to cooperate with each other in accordance with natural law. Until relatively recently, it was always understood that any system of property, marriage, or contract required formalities to verify that the appropriate rights were properly observed. Similarly, no one ever thought that these rights were so absolute in their inception that they could not be limited for good reason in particular cases. Indeed, the entire structure of the pleading laws, which built in ample room for excuses and justifications, built high levels of flexibility into the basic system.