In 2001, the U.S. House of Representatives passed the "Human Cloning Prohibition Act" and President Bush announced his decision to allow only limited research on existing stem cell lines but not on "embryos." In contrast, the U.K. has explicitly authorized "therapeutic cloning." Much more will be said about bioethical, legal, and social implications, but subtleties of the science and careful definitions of terms have received much less consideration. Legislators and reporters struggle to discuss "cloning," "pluripotency," "stem cells," and "embryos," and whether "adult" are preferable to "embryonic" stem cells as research subjects. They profess to abhor "copying humans" or "killing embryos." Do they know what they are talking about? Do we? This paper explores the historical, philosophical, and scientific contexts that inform this heated discussion.