0:00:14 > 0:00:17- This is Dave.- Hi!
0:00:17 > 0:00:19Dave owns a wooden ship, called the Theseus.
0:00:19 > 0:00:21And that's Dave's wife.
0:00:21 > 0:00:24- SHE SOBS - She doesn't like goodbyes.
0:00:24 > 0:00:25Dave and his crew...
0:00:25 > 0:00:27- ALL: Oooh, arr! - Yes, thank you.
0:00:27 > 0:00:31Dave and his crew are setting off on a long voyage.
0:00:31 > 0:00:34It's a tough voyage with many storms and mishaps.
0:00:34 > 0:00:37And it gets really quite hard to keep the ship sailing
0:00:37 > 0:00:40and to stop bits of it falling into the water!
0:00:40 > 0:00:43THUNDER
0:00:43 > 0:00:44Every time the ship is damaged,
0:00:44 > 0:00:47Dave takes the Theseus to George's shipyard
0:00:47 > 0:00:50and George replaces the broken wooden bits
0:00:50 > 0:00:52with shiny, new metal ones.
0:00:53 > 0:00:55Bye.
0:00:57 > 0:01:00But there are many dangers, like Olly the octopus,
0:01:00 > 0:01:03who does like a bit of fish and chips.
0:01:06 > 0:01:08And so every few months of his journey,
0:01:08 > 0:01:10Dave heads back to see George
0:01:10 > 0:01:13and has any broken wooden bits replaced with metal.
0:01:13 > 0:01:16- Bye-bye.- Bye.
0:01:16 > 0:01:17DAVE HUMS
0:01:17 > 0:01:20And each time the ship gets damaged...
0:01:20 > 0:01:24- TWANGING - ..more metal parts are added, and so on,
0:01:24 > 0:01:27and so on, until eventually,
0:01:27 > 0:01:30every part of the Theseus has been replaced.
0:01:30 > 0:01:33The ship is now entirely metal, inside and out.
0:01:35 > 0:01:37When Dave gets home, his wife,
0:01:37 > 0:01:42who's been really missing Dave a great deal, is surprised.
0:01:42 > 0:01:43Hmm...
0:01:43 > 0:01:45She wants to know why he's got a new ship.
0:01:45 > 0:01:48"I haven't got a new ship," says Dave.
0:01:48 > 0:01:51Dave's wife insists that it can't be the same ship.
0:01:51 > 0:01:54Dave insists that it is.
0:01:54 > 0:01:58This goes back and forth for what seems like an eternity.
0:01:58 > 0:02:00But Dave's wife won't budge.
0:02:00 > 0:02:03"Your ship was wooden, and this ship is metal.
0:02:03 > 0:02:06"Nothing of the old ship remains."
0:02:06 > 0:02:07What do you think?
0:02:15 > 0:02:17MUSIC DROWNS SPEECH
0:02:24 > 0:02:27It's the same ship because it's still got the same structure,
0:02:27 > 0:02:29it's just made of different materials.
0:02:29 > 0:02:31It's not really the same ship
0:02:31 > 0:02:33because he's literally just rebuilt the ship.
0:02:33 > 0:02:36He's made, like, a different ship.
0:02:36 > 0:02:39Well, he'll still have the memories of the ship,
0:02:39 > 0:02:41so it would be the same ship to him
0:02:41 > 0:02:44even if it didn't have the same things inside.
0:02:51 > 0:02:56I think, um, it became a different ship when the last piece was put in.
0:02:56 > 0:03:00Because when it had the old pieces, before the metal ones,
0:03:00 > 0:03:02he still had one bit of the old ship.
0:03:02 > 0:03:04But once it had been replaced with metal,
0:03:04 > 0:03:07he would have completely rebuilt the ship.
0:03:07 > 0:03:12I agree with Lowri because, first of all, it was the same ship
0:03:12 > 0:03:14because there was still bits of wood.
0:03:14 > 0:03:19Now, because it is all metal, it is not the same ship any more.
0:03:24 > 0:03:27Dave and his wife haven't stopped arguing about whether it's
0:03:27 > 0:03:29the same ship when, suddenly,
0:03:29 > 0:03:32over the horizon, a familiar shape appears.
0:03:32 > 0:03:34It is the Theseus,
0:03:34 > 0:03:36only made of wood.
0:03:36 > 0:03:37How did this happen?
0:03:39 > 0:03:44It turns out, George always wanted his own ship
0:03:44 > 0:03:47so, rather cleverly, he kept all the wooden bits
0:03:47 > 0:03:50that fell off the original Theseus and decided to rebuild it.
0:03:50 > 0:03:54It needed a lot of hard work and an awful lot of nails.
0:03:54 > 0:03:58But it looks very good now he has finished.
0:03:58 > 0:04:01The minute she sees the ship, Dave's wife thinks it is Dave's ship,
0:04:01 > 0:04:03the Theseus.
0:04:03 > 0:04:05So, what does this mean?
0:04:05 > 0:04:09They are both called the Theseus and they both look the same.
0:04:09 > 0:04:13Well, except that one is made of wood and one is made of metal.
0:04:13 > 0:04:16It's all getting a bit confusing.
0:04:16 > 0:04:18Oh, dear.
0:04:31 > 0:04:35If you got a house and you took off all the pieces
0:04:35 > 0:04:39and put a new house and then someone else took the old pieces
0:04:39 > 0:04:40and built a new house,
0:04:40 > 0:04:45it would be a different house so the same way of the ship.
0:04:45 > 0:04:49That, the metal one, is the Theseus
0:04:49 > 0:04:52and the wooden one is a copy of it.
0:04:53 > 0:04:58I'm not really that sure because the wooden one that George has
0:04:58 > 0:05:03is made out of the proper things that the old Theseus was made of
0:05:03 > 0:05:07but then the one Dave has is still the Theseus
0:05:07 > 0:05:11but it is made of metal and so it is like there is two the Theseuses.
0:05:11 > 0:05:13In a way.
0:05:13 > 0:05:18The person who bought the boat or made the boat
0:05:18 > 0:05:22was Dave so he named the boat
0:05:22 > 0:05:27so if someone else was going to call their boat the Theseus
0:05:27 > 0:05:31then it wouldn't be the same boat just cos it had the same name.
0:05:31 > 0:05:33It might look the same but it is not
0:05:33 > 0:05:37cos someone else bought it so it is owned by someone else.
0:05:41 > 0:05:44Now, this is all very well with ancient ships and whatnot
0:05:44 > 0:05:48but what happens if we think about something a little closer to home?
0:05:48 > 0:05:51Like...I don't know...you.
0:05:51 > 0:05:53You see, like Dave's ship,
0:05:53 > 0:05:56our bodies change and grow throughout our lives.
0:05:56 > 0:05:59We are born, we grow up into toddlers
0:05:59 > 0:06:03then children and we keep growing into teenagers
0:06:03 > 0:06:07then adults and we continue changing our whole lives.
0:06:07 > 0:06:10Our hair grows and falls out and more grows without us
0:06:10 > 0:06:16even noticing. We get a whole new set of teeth. Everything changes.
0:06:16 > 0:06:20So, if every part of us gets replaced too, like Dave's ship,
0:06:20 > 0:06:22then that raises a big question.
0:06:32 > 0:06:36Your body might have changed but you still are the same person.
0:06:36 > 0:06:41You have still got all the outside qualities
0:06:41 > 0:06:45like your personality and what you would be.
0:06:45 > 0:06:49You are of the same person because organs are the same
0:06:49 > 0:06:54and personality is the same so, if your cells change,
0:06:54 > 0:06:57it's not the whole person which has changed.
0:07:04 > 0:07:07Subtitles by Red Bee Media Ltd