Modern technology has made it possible for physicians to save lives that even just a few years ago would have been lost. Although such medical advances have given us many reasons for celebration, they have also rasied a variety of questions about whether the essence of life should be maintained if the quality of life is lacking. That is, are patients whose bodies are being kept alive by machine, although they will never recover to lead a normal life, truly enjoying life?

In response to cases such as that of Karen Ann Quinlan, a New Jersey woman who lingered in a coma for 10 years after drinking alcohol mixed with a small amount of Valium and Librium, the medical and legal communities devised the advance directive. An advance directive allows a person---before he or she enters surgery...