The relationship between identity and change in the philosophical field of metaphysics seems, at first glance, deceptively simple, and belies the complexity of the issues involved. This article explores "the problem of change and identity".
When an object changes, it always changes in some particular way. A baby grows up, and so changes in respect of size and maturity; a snake sheds its skin, and so changes in respect of its skin. "Change" may therefore be defined as follows:
That seems to be, in one way, what it means for a thing to change: it has a property at one time, and later it does not have that property. If a banana becomes brown, it can then be said: at one time, the banana is yellow; several days later, the banana is not yellow, but is instead brown. This appears fairly straightforward at this point, and there are no apparent problems as yet.
Another way for an object to change is to change its parts.
Some philosophers believe that an object can't persist through a change of parts. They defend mereological essentialism.
Problem of change
The question then arises as to what sort of change happens after a thing is destroyed? When a person dies, one does not say that the person's life has changed. Neither does one go around saying, "Harry just isn't the same sort of guy since he died." Instead, one says that Harry's life has ended. Similarly, when a building is demolished, one does not say that the building 'changes'; one says that it is destroyed. So what sort of events, on the one hand, result in a mere change, and what sort of events, on the other hand, result in a thing's destruction — in the state of its existence? This is one aspect of the problem that will be considered here. It is called "the problem of change and identity".
The Ship of Theseus
The "problem of change and identity" is generally explained with the story of the Ship of Theseus:
There is one answer which is a little too easy and quick. One might say: "No, of course not. The Theseus has changed a lot, so it's not the same ship. At the end of your life, you're not going to be the same person as you were, when you were a teenager. You're going to change a lot in the meantime." However, this is not quite answering the intended question. What is intended by the question is the sense of the word, "same", in which an old woman is the same person at the end of her life as she is, at the beginning of her life. Certainly, the word, "same", has such a sense. After all, one implicitly depends on it when one says, for example, "She has changed a lot". In order for someone to change a lot, there has to be one person who underwent the change. (One could perhaps reject that sense, saying that objects do not change over time.)
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