This article has two purposes. The first is to show how one can know in a simple way what is an ordinary and obligatory means to care for a person with a serious illness. Using the information at hand, one must be able to answer yes to each of these three questions: “Is this the ordinary, usual, or valid way of treating this illness?” “Is it working?” “Is it within the capacity of the patient to undergo and of the caregivers (...) to administer?” The second purpose of the article is to show the moral validity of these questions, using a historical overview of theological and magisterial teaching and a systematic analysis and moral testing of the three questions. (shrink)