In response to the responses to Bob's query about what our readers want us to write about -- and here I thought I started a blog so that I could write about whatever the heck I wanted to! -- I post a genuine philosophical puzzle, and one which I really don't know how to answer.
The paradigmatic example of the conundrum is 'the ship of Jason' (of Argonaut fame). Suppose at time x we can uncontroversially identify ship A as 'the ship of Jason'. But time passes. Gradually the Argonauts and their successors replace more and more components of the ship with newer instances of the same part. Finally, the day comes when every single bit of ship A that made it up at time x is gone. Is the vessel in question still the ship of Jason?
Next, let us imagine that someone scavenges all of the discarded pieces of the ship that had comprised it at time x, and uses them to assemble a second, perhaps somewhat decrepit, ship, and at time y proclaims 'Behold the ship of Jason'! If you decided that the totally refurbished ship introduced in the previous paragraph was still 'the ship of Jason', then what do you make of this new claimant to the designation? It, after all, is made up of precisely the same components as the ship that we agreed clearly was the ship of Jason at time x. It seems an abuse of common usage to hold that at time y there exist two ships of Jason, even though Jason himself had but one while he was alive. Nevertheless, we have at hand a pair of craft either of which, in the absence of the other, we would probably regard as sensibly designated 'the ship of Jason'. So how to resolve the embarrassment of there being two such vessels?
The puzzle does not, of course, only arise with regards to inanimate objects, and the problems to be solved by any philosophical analysis of person-hood are probably readily apparent. If you happen to be a materialist who still posits the real existence of individual human agents, then you are tasked with explaining why you are justified in talking about the 'same' person across a lifetime when that 'individual' at 70 is composed of entirely different bits of matter than she was at 10. If, on the ohter hand, you contend that there is some constant spiritual essence animating and uniting all of the diverse physical manifestations of 'an individual', then you face the difficulty of explaining how such an immutable entity can have any connection whatsoever with the ever-changing attributes of people as we un-philosophically experience our acquaintances in day-to-day life. At least at first glance, such an eternal absolute would seem to be categorically immune from being effected by temporal happenings, just as the Pythagorean Theorem is not impacted by the outcome of a war or the results from an election. Quite to the contrary, our 'folk' understanding of our fellow humans conceives them as continually transforming per the influence of new experiences. However, if that picture is mostly correct, then where is the enduring 'person' whom we are inclined, for instance, to hold responsible for a crime? If 'Joe 2008' contends he is 'a whole new man' from 'Joe 2007' who committed a murder, then, absent any plausible notion of how they are really still the 'same individual', how can we justify punishing 'Joe 2008' for a transgression of 'Joe 2007'.