So, are you identical twins?

Hello,

Have you heard of the Ship of Theseus? Well this is it...According to Greek legend (reported by Plutarch, a Roman citizen)

                                                                 

The ship wherein Theseus and the youth of Athens returned [from Crete] had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their place, insomuch that this ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other arguing that it was not the same.

-Plutarch, Theseus

Plutarch then wonders if the ship would remain the same if the ship was entirely replaced, plank by plank, as a proposition, you can question what happens if the replaced parts are used to build a second ship? Which, if either, is the Ship of Theseus? The Ship of Theseus is an example of the problem of identity, the original crisis of Identity. But philosophers have been working on such crises and have created 'proposed resolutions'. I will focus on the difference of 'same'. It is a way of differentiating the same and one and the same. 

Essentially there are two definitions of 'same'. The first of which being qualitatively the same, meaning the same properties or qualities. 

The second being numerically the same, so they are actually one and the same.

For example: Tweedel-dee and Tweedel-dum are qualitatively the same as they look identical (and also both very annoying) but they are not numerically the same as they are different people.

So when is an an object numerically the same? (one and the same). The following is an example. You start with two identical black bikes, (qualitatively the same), they would not be numerically the same. But if you painted one of the bikes red... the red bike would no longer qualitatively the same as the black bike but it would be numerically the same to it's previous form. 

So basing your answer on the idea of qualitative and numerical 'same' you can answer the original question: Which is the Ship of Theseus? The ships are  the 'same'. They are qualitatively different as they are made out of different planks, but are numerically the same - just like the bike is the same, only a different colour.