The ship begins a voyage around the world and in the course of this voyage some of the parts of the ship inevitably break. One by one, the broken parts of the ship are replaced with new parts that are similar to the original parts. By the time the ship returns home at the port, all parts have been replaced after breaking down one by one. From the framing to the deck to the last bolt and nut, everything has been replaced. Even the painting is new. The question that begs is whether this ship is the same or it is a different ship. This is a tricky question bearing in mind that meaning all the parts of the ship have been replaced at the end of the long voyage meaning that the original outlook has been changed. The original structure has also been changed with parts that are identical to the original parts. Is this ship a different one or the same old ship that left the port for the voyage? To start with, it is important to note that if one looks at the ship when it lands back at the port, it is almost impossible to note that the ship has undergone replacements because the parts that have been used to replace the original parts are identical to the replaced part. The name of the ship and the registration has not changed and what have changed are the parts that initially made up the ship. The whole ship has changed, from the largest part to the smallest nut in the ship. The problem is that people cannot notice the difference because the parts used are quite identical and this brings this discussion to a new realm where we ask ourselves some pertinent questions.
One of the most important questions is: just because people cannot notice the difference because identical new parts have been used, does this mean that the ship is still the same one? Surely, this is not the ship that left the port. The parts that made the initial ship are absent in the ship that arrives at the port. The entire structure and composition have changed and changing the entire structure of the ship by putting new parts are the same as buying a new ship and putting the registration number of the old ship. The cost of replacing every part is almost the same as buying an entirely new ship. Though people may not see the difference, it is evident that the ship that returns to the port is not the ship that left the port. The entire framework of the ship that left the port has been replaced with a new one. The ship that left the port is no more since all its parts including the casing lay somewhere as scrap materials meaning that at the port we get an entirely new ship. From a mechanical perspective, we can argue that the ship has been renovated but from a psychological perspective, the most plausible argument would be that the ship that left the port is not the ship that docks the port at the end of its voyage.