You have no doubt heard this example of the problem of identity before, but bear with me.
Say you are given an axe for your birthday. Upon using the Axe on a length of wood you smash the axe head on a rusty bolt. You venture to get another Axe head from your local hardware store, return home and replace the damaged part with the new. Upon striking the wood a second time you consciously avoid the bolt to no avail as now the Axe handle shatters. You, for a second time, venture to the hardware store to get a replacement handle, return home and install it. Now, the question you probably saw coming is – is this still the Axe you were given for your birthday? I say yes, because you attached the
replacement parts with respect to its original condition, not with intent to modify or improve. The deeper problem with saying that, indeed, the Axe SHOULD now be considered a
different Axe is that the human body replaces all its atoms every 7 years (or so), yet nobody says that we are doppelganger (many times over)...