h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

The suggestion that one-to-one replacement of parts allows an item or organism to remain unchanged, implies that, if those same replacement parts were to be assembled without the interposed replacement act, you would end up with the "same" entity. The problem, as I see it, is in the definition of the word "same".

A photo-copy of a document is not identical, I think we can all agree. But a photo-copy of a photo-copy, using the identical paper, toner, exposure, etc., is still another copy and not the same copy. This would be true even if it were a copy-of-the-copy below the molecular level.

What is being discussed is the sneaky copying, accompanying the destruction of the original which then exists no more. Therefore it can be "identical", but cannot be the "original".

It sounds a lot like discussions on the ethics of Star Trek like transporter beams. The "original" is scanned, and destroyed in the process. The "pattern" is stored during transmission, and "reassembled" from matter on the other end. One is perpetually making a supposedly identical copy from the original scanned blueprint; but a copy, nonetheless. (Amazing that so few transporter accidents end up making more than one reassembly!)

The "copy" has all the traits, memories, and attributes of the orignal, and believes itself to be so. It is accepted as such, not because it "is" the original, but because the lack of differences (and the lack of an existing original) make the point moot. It is as sufficient as having had the original delivered in a shuttle. Amazing what our future selves might be willing to endure for quick, cheap travel.