This isn't that, though. They're not replacing the bridge strand-by-strand; they construct an entirely new bridge each year then get rid of the old one.

They use the old bridge to bootstrap the new bridge, by pulling the new ropes across. Each bridge is a descendent of the previous bridge. The continuity makes a "500 year old bridge".

These bridges were intended to be temporary, whereas stone or metal bridges are intended to be permanent. You are comparing apples to oranges.

The new bridge and the old bridge are actually the same bridge, just made with different materials.

This is like the Platonic HN comment. Person hears about an interesting problem in another field (yeah, the ship of Theseus is actually interesting. That's why people still discuss it), asserts the solution after having thought about it for two minutes, then provides a useless analogy. Good work, you solved the problem! All those philosophers can quit their adjunct professorships and go bootstrap some social web companies now.

...no, the point was that it wasn't a ship of theseus situation.

Ironically, the same people complain about the Microsoft-style interview questions that require lateral thinking.

"How many gas stations are there in _your city_?"

"How would you determine how much rain falls in Washington State in a day?"

The person metaphor works if you consider the purpose instead of the individual.

There has been a mayor of New York since the mid 1600s, though the individual fulfilling that role has changed regularly.

Similarly, there has been a bridge on this stretch of gorge for some time, though the expanse must be replaced regularly.

Yes, but the 'bridge,' in this case, is more akin to the mayor not the mayorship.

It's more like a house blown over in a hurricane. It gets rebuilt, but the land and foundation and some other infrastructure might be re-used --it's still not the 'old house' --it's the re-built house.

>It'd be like claiming the different people that inhabit the same house over the span of 100 years are all the same people, because they're all humans. They're all people, and they all inhabited the house ('the people in that house'), but they in fact possess different unique identity.

If it was the same family or if they shared a few genetic markers that distinguished them from other peoples in the area... then you could say the same people had lived at ________ area.

In that case, it's like the Ise Grand Shrine in Japan. On the one hand, it's over a thousand years old. On the other hand, it is rebuilt every 20 years by the monks. So how old is"The Shrine"? http://en.wikipedia.org/wiki/Ise_Grand_Shrine#Rebuilding_the...

I am going to go with "20 years old". The current shrine is scheduled to be torn down this year.

..and one hand makes no sound, obviously.