"The term persona comes to us from the Roman and Etruscan theater, where it denoted the mask worn by the actor and therefore the character whom the actor portrayed. The term was borrowed by Roman law to describe any entity that has judiciable rights and duties, including corporate entities and other more abstract constructions. It was borrowed again by early Christian theologians in order to explain the doctrine of the Trinity, by distinguishing the three persons of God. Discussions of the Trinity led to the view that personhood belongs to the essence of whatever possesses it, and the sixth-century philosopher Boethius took this as his cue in defining the essential nature of the human being. For Boethius the human person is "an individual substance of a rational nature."19 That definition was adopted by Aquinas and remained in place until the Enlightenment, when two great philosophers--Locke and Kant--saw fit to reexamine the whole idea and untangle its many strands. According to Boethius's"