Identity

My father replaced the lenses on his glasses. Then he replaced the frame when it later broke. Same type of lenses and same model of frame. He claims they're still the same pair of glasses. When I argue he's wrong and that they're now a different pair, he claims the same could therefore be said of him as he's replaced all his cells several times since he originally bought the glasses but, since he's still him, the glasses are still the glasses. Who's right?

Comments

"Is the same as" is ambiguous. It could mean "same thing" or "same kind of thing" or even "same thing but not necessarily same stuff". Your father is speaking in the last sense--the glasses look the same, and moreover, the 3 pairs of glasses are built through successive fixes. You can avoid the verbal paradox by asking "the same in what respect?" The glasses are not the same stuff, and they do not have all the same physical properties (such as weaknesses in the glass and frame) but they are the same style and they are constructed successively out of one another.

A CLASSIC case! This is a major issue going back to ancient philosophy. The example used then was the ship of Theseus (a Greek hero). Imagine you have the ship of Theseus and a similar ship side by side. First you switch one part (the mast, say). Is the ship of Thesus still the same? Many of us want to say 'yes,' but then we get puzzled as more and more parts are switched until eventually it seems the ships have changed places. One route that philosophers have taken might bring peace to your family: some philosophers distinguish a strict sense of identity from an identity that is "popular and loose." On a strict view, you are right. Any object with parts is not the same if even a single part is removed. This is technically called mereological essentialism. According to mereological essentialism, your father's body today is not identical with the body he had as a boy. You might even suggest to him that while he went to first grade, that (pointing at his body) did not. You can retain mereological essentialism while also allowing that sometimes we can and should meaningfully speak of sameness of identity that is not strict. In the later, though, there will be different conventions that come into play. So perhaps there is a way to allow that you both may be right? If push comes to shove, however, I am on your side on this. For a defense of our view, see the book Person and Object by Roderick Chisholm.

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