 Other issues in the ontology of law pertain to the nature of entities that pervade the law, such as contracts (Fried 1981, Barnett 1985, Hart &amp; Holmstrom 1986), promises (Scanlon 1990, Kolodny &amp; Wallace 2003, Owens 2006, Shiffrin 2008), and torts (J.L. Coleman 1982, 1983, Postema 2001). The law also plays a central role in setting up certain social categories, such as marriage and corporations. Marriage is tightly regulated by the law in many cultures. Does the law define what marriage is, or is marriage set up wholly or in part by social practices? Likewise for corporations: does the law have a privileged role in determining what types of corporations exist in a modern society, or are corporations products of social and economic systems? (See  section 5.3.)