  The philosophical puzzle regarding advance directives is  fundamentally a puzzle about personal identity. Suppose that a woman  is in the earliest stages of Alzheimer's disease, and she recognizes  that there will come a point where she is in a demented state and  will thus be incompetent to make autonomous or informed decisions  about her treatment. Because she values her creativity and autonomy,  she does not want that future demented self to be kept alive –  its life will not be worth living – so she signs an advance  directive stipulating that no life-saving measures are to be used on  that future demented self (FDS). However, by the time her FDS gets  pneumonia, she is quite content in her state and, when asked, says  she wants to live (e.g., McMahan 2002, 497).