Many debates in biomedical ethics today involve inconsistencies in defining the key term, person. Both sides of the abortion debate, for instance, beg the question about what constitutes personhood. This book explores the arguments concerning definitions of personhood in the history of modern philosophy, and then constructs a superior model, defined in terms of distinctive features (a theoretical concept borrowed from linguistics). This model is shown to have distinct advantages over the necessary and sufficient condition models of personhood launched by essentialists. Philosophers historically have been correct about what some of the pivotal distinctive features of personhood are, e.q., rationality, communications and self-consciousness, but they have been wrong about the methods of recognizing and asserting personhood, and about the relative importance of feelings. In clinical care, complaints often surface that care is not personal. This book aims to improve care through providing a method of attending to patients as people. Charts in the Appendices show that where physicians attended to personal features important to their patients, sometimes the patients rated the care even higher than the physician did. The book will be useful to health-care providers whose goals include improving quality of care, listening to patients, and preventing malpractice.