The law has a long-standing habit of pretending: that an adopted child is the natural child of the adoptive parents, that a registered company is a person capable of suing and being sued. Sir Henry Maine, in Ancient Law (1861), called the legal fiction one of three great agencies, alongside equity and legislation, by which law adapts to changing societies, tracing it to the Roman fiction.
The device has not been universally welcomed; historically, jurists worried that fictions allowed judges to make law in disguise. Lon Fuller, in his Stanford monograph Legal Fictions (1967), laid down the modern test: a fiction is honest only when its falsity is openly acknowledged; once it is “taken seriously”, once people begin to treat the pretence as fact, it loses its utility and becomes dangerous. A fiction is a tool, fashioned for a defined end, and works only within that end.
