Relativism and persistence

[FIRST PARAGRAPHS] Philosophers often talk as if what it takes for a person to persist through time were up to us, as individuals or as a linguistic community, to decide. In most ordinary situations it might be fully determinate whether someone has survived or perished: barring some unforeseen catastrophe, it is clear enough that you will still exist ten minutes from now, for example. But there is no shortage of actual and imaginary situations where it is not so clear whether one survives. Here reasonable people may disagree. There are "fission" cases where each of one's cerebral hemispheres is transplanted into a different head; Star-Trek-style "teletransportation" stories; actual cases of brain damage so severe that one can never again regain consciousness, even though one's circulation, breathing, digestion, and other "animal" functions continue; and stories where one's brain cells are gradually removed and replaced by cells from someone else, to name only a few favorites. In many such cases we say, correctly, that the person in question has perished; that is the right answer to the question, Has she survived? But in some of those very situations, we are told that it might have been correct to give the opposite answer, and say that the person perished--even if nothing different happened to her. Some philosophers say that we are free to choose at random between saying that the person has survived and saying that she has ceased to exist; both are equally correct descriptions of the same event. Others say that a different answer to the question, Has the person survived? is in fact false, but would be true if we had a different concept of personal identity, or if our conventions for individuating people were different--in short, if we thought and spoke differently.