The combined spectrum Notes for November 30

Main points

Parfit argues that questions about personal identity do not necessarily have determinate answers. He does so by asking us to consider a spectrum of cases in which a person changes in a variety of ways.

Let’s call the person after the changes have been made B and the person before the changes are made A. After considering each change, we can ask “Is B the same person as A?” In many cases, the answer will be “yes” or it will be “no.” The conclusion Parfit hopes to establish is that there are some changes for which it is equally appropriate to say “yes” or “no” or even “yes and no.”

Parfit believes that this is a consequence of the Psychological Criterion of personal identity, the Physical Criterion of personal identity, or any combination of the two criteria. But, he believes, it is a consequence that those who propose these criteria have failed to appreciate. He is less interested in finding the true criterion of personal identity over time than he is in establishing his point about the possible indeterminacy of personal identity.

I said that I found that conclusion intolerable but, at the same time, that I could not see how to resist it.

The Ship of Theseus

Harley mentioned this a couple of sessions ago. Hobbes introduces the example to show that the identity of a thing does not always consist in its form. A form, in turn, is supposed to be something that explains how it is possible for one continuous thing to be made up of changing matter. A ship remains over time, the story goes, so long as the various bits of matter that make it up have the same form that makes them part of one ship.

The idea of a form is both sensible and elusive. It makes sense to say that changing bits of matter can be part of one thing so long as they are organized in a particular way, but it’s hard to know just what the heck a form is or how it could play a role in organizing matter. Anyway, Hobbes has his own objection, based on the example of the ship.

Hobbes’s term “accident” means, roughly, properties or things you can perceive.

But the same body may at different times be compared with itself. And from hence springs a great controversy among philosophers about the beginning of individuation, namely, in what sense it may be conceived that a body is at one time the same, at another time not the same it was formerly. For example, whether a man grown old be the same man he was whilst he was young, or another man; or whether a city be in different ages the same, or another city. Some place individuity in the unity of matter; others, in the unity of form; and one says it consists in the unity of the aggregate of all the accidents together. For matter, it is pleaded that a lump of wax, whether it be spherical or cubical, is the same wax, because the same matter. For form, that when a man is grown from an infant to be an old man, though his matter be changed, yet he is still the same numerical man; for that identity, which cannot be attributed to the matter, ought probably to be ascribed to the form. For the aggregate of accidents, no instance can be made; but because, when any new accident is generated, a new name is commonly imposed on the thing, therefore he, that assigned this cause of individuity, thought the thing itself also was become another thing. According to the first opinion, he that sins, and he that is punished, should not be the same man, by reason of the perpetual flux and change of man's body; nor should the city, which makes laws in one age and abrogates them in another, be the same city; which were to confound all civil rights. According to the second opinion, two bodies existing both at once, would be one and the same numerical body. For if, for example, that ship of Theseus, concerning the difference whereof made by continual reparation in taking out the old planks and putting in new, the sophisters of Athens were wont to dispute, were, after all the planks were changed, the same numerical ship it was at the beginning; and if some man had kept the old planks as they were taken out, and by putting them afterwards together in the same order, had again made a ship of them, this, without doubt, had also been the same numerical ship with that which was at the beginning; and so there would have been two ships numerically the same, which is absurd. But, according to the third opinion, nothing would be the same it was; so that a man standing would not be the same he was sitting; nor the water, which is in the vessel, the same with that which is poured out of it. Wherefore the beginning of individuation is not always to be taken either from matter alone, or from form alone.

But we must consider by what name anything is called, when we inquire concerning the identity of it. For it is one thing to ask concerning Socrates, whether he be the same man, and another to ask whether he be the same body; for his body, when he is old, cannot be the same it was when he was an infant, by reason of the difference of magnitude; for one body has always one and the same magnitude; yet, nevertheless, he may be the same man. And therefore, whensoever the name, by which it is asked whether a thing be the same it was, is given it for the matter only, then, if the matter be the same, the thing also is individually the same; as the water, which was in the sea, is the same which is afterwards in the cloud; and any body is the same, whether the parts of it be put together, or dispersed; or whether it be congealed, or dissolved. Also, if the name be given for such form as is the beginning of motion, then, as long as that motion remains, it will be the same individual thing; as that man will be always the same, whose actions and thoughts proceed all from the same beginning of motion, namely, that which was in his generation; and that will be the same river which flows from one and the same fountain, whether the same water, or other water, or something else than water, flow from thence; and that the same city, whose acts proceed continually from the same institution, whether the men be the same or no. Lastly, if the name be given for some accident, then the identity of the thing will depend upon the matter; for, by the taking away and supplying of matter, the accidents that were, are destroyed, and other new ones are generated, which cannot be the same numerically; so that a ship, which signifies matter so figured, will be the same as long as the matter remains the same; but if no part of the matter be the same, then it is numerically another ship; and if part of the matter remain and part be changed, then the ship will be partly the same, and partly not the same.** Thomas Hobbes, Elements of Philosophy (1655) Part II, Ch. 11, §7.

Note the last sentence in the second paragraph. That’s the sort of thing that Parfit thinks it is possible to say about people.

This page was written by Michael Green for Problems of Philosophy, Philosophy 1, Fall 2009. It was posted November 30, 2009.
Name of website