The problem here is one of medical limitations as well as ethics. If there is absolutely no possibility of the person ever being more than a ‘cabbage’, then life for that person serves no purpose. There is such a thing as a living death. The difficulty is that it is not always possible for a medical man to state authoritatively that there is absolutely no hope. Also, medical science is continually advancing, coming up with new answers. The proper answer surely should be, when life becomes purposeless and valueless to the patient, without any hope of amelioration and he or she can no longer participate in the lessons of life, then life should not be maintained by electronic, mechanical or chemical means.