A legal fiction is a fact that is assumed or created by courts in order to apply a legal rule. Most often a feature of common law systems, perhaps the best-known (and one of the most controversial) such fictions in the U.S. is the concept of corporate personhood. A long-standing rule was that only persons could sue or be sued; with the growth of corporations after the Industrial Revolution a legal fiction was created that corporations were also persons, thereby allowing corporations to be held liable for their debts. For another example, see my blog post on adultery law.