In the Star Trek universe eight starships bearing the name Enterprise have appeared on screen or been referred to in some way (a count that does not include ships in or from alternate realities or universes). In our actual world (between the year 1704 and the present) there are over more than two dozen commissioned and non-commissioned naval vessels named Enterprise. Most have been seagoing vessels, but the list includes a space craft and a Civil War hot air balloon. Some of these ships were originally christened ‘Enterprise’ while others were captured vessels which were renamed. The British and the United States navies have had at least one vessel named Enterprise in service since 1776.
The continued use of a single name for successive vessels is an ancient naval tradition; a tradition meant to carry the legacy of a vessel, but not a claim of numeric identity. No one with working eyes could possibly look at the 1776 U.S.S. Enterprise, a schooner, and mistake it for the 1960 U.S.S. Enterprise, a nuclear aircraft carrier.
The U.S.S. Enterprise aircraft carrier was in active service from 1961 to 2012 (and inactive service until 2017). Though it was state of the art at the time it was launched, it would not have stayed state of the art without significant retrofits, refits, and modifications during its 50-year plus history. Though it underwent significant changes throughout its lifetime we still refer to the Enterprise circa 1961 and the Enterprise circa 2012 as one and the same ship. But is this really the case? How much change can a thing undergo and remain the same thing?
This is a very old question in philosophy. The pre-Socratic philosopher, Heraclitus, said:
Both rivers and humans (and every other physical thing) are in a constant state of change. Though water might follow the same path for millennia, it is never the same water forming the same waves and ripples from one moment to the next. Human beings are always exchanging matter with the world through respiration, perspiration and other “ations” not quite so polite. From this fact, Heraclitus drew the conclusion that nothing remains the same thing from moment to moment.
A later Greek philosopher (and later Roman citizen), Plutarch, formulated perhaps the most famous (or infamous) version of this dilemma in the form of the “Ship of Theseus”. There are nearly as many variations of this thought experiment as there are philosophers debating it, but the short version is this: how many changes can you make to a ship before you have to say it is a different ship? Is it when you change out one rope? More than half of the parts? All the parts?
We can ask a similar question in the Star Trek universe. There are six ships with the designations NCC 1701 (the “1701-J” is not being counted in this case). When an Enterprise is decommissioned, destroyed, or a combination of the two, another ship is constructed to take its name, or an existing ship is renamed in its honor. The fates of the six starships named Enterprise are almost all spelled out either explicitly or implicitly. In all these cases one ship was taken out of service, by some means or other, and the next was launched having had the next letter of the alphabet added to its registry number, each ship being a distinct thing from its predecessors and descendants. But what do we say of the NCC 1701 pre- and post-refit? (from this point on I will refer to these ships, or stages of the ship, as ‘1701’ and ‘*1701*’ respectively). Is the Enterprise a different ship or the same ship after having undergone such significant changes? What are the arguments that it remains the same ship and what are those that it is different? The principle of the question is no different than the question raised by Plutarch’s thought experiment. The only difference is that Plutarch’s ship of Theseus was made of wood and propelled by wind harnessed by linen sails and the 1701 is built of stronger stuff and “sails” in a vacuum between the stars. This ancient question has many defensible answers but not a single definitive one. What are the answers that have been given and what are the strengths and weaknesses of them?
All physical things undergo change over time and the Enterprise is no exception. I am not willing to go as far as Heraclitus and claim that from any moment to the next 1701 is different if any single change in physical substance has taken place. During the run of TOS it does not take long for the 1701 to suffer hull breaches requiring patching or a warp drive in need of maintenance, but perhaps not even these are enough to make the 1701 a different thing entirely. However, the refit which took place between the events of the final TOS episode (Turnabout Intruder) and TMP made substantial changes to the shape, layout and even size of the ship.
What are we to say about the identity of the 1701 in this case? Let’s assume for a moment that the 1701 and the *1701* are one and the same ship. That ship was scuttled by Kirk in TWOK and was replaced by the 1701-A. The *1701* and the 1701-A are different ships owing to the fact that they have completely different histories. Their construction began at different times and the 1701 had a long life even before the first bulkhead of the 1701-A was laid down. This isn’t that much different than going to a car lot and trading in your high-mileage ride for a newer model. In a sense, all of the *1701*’s parts were changed at once and this new ship is called the 1701-A. Call this the ‘whole-hog approach”.
The whole-hog approach is not what we are taken to believe happened to the 1701. Rather, the 1701 systematically had parts removed, replaced, and reoriented. Call this the “piecemeal approach”
Does the 1701 survive this kind of piecemeal change of parts over time? If not, when does the 1701 become a different ship?
There are only three points during the removal and replacement process that one can draw a principled line and say ‘here it is now a different ship’: 1- when the first piece is replaced, 2- when more than 50% of the ship has been replaced (call this the 50%+1 threshold), and 3- when all the ship’s parts have been replaced. Drawing lines anywhere else would be arbitrary and lead to quibbling about what the different between what is, say, 41% and 41.5%. Let’s consider each of these three points in turn:
The ship is a new ship as soon as any part has been changed
As with the Heraclitan claim that no man ever steps into the same river twice, this position would mean that nothing is ever the same from one moment to the next. If a hair falls out of my head, I am a new person. When I drive my car, I leave imperceptibly small pieces of rubber on the road and new materials get stuck in the radiator grate, thus resulting in a ‘new’ car in every time interval shorter than a stroke of the engine. In the case of the 1701, once Scotty replaced a dilithium crystal, or reran a frayed wire, the ship would be a new thing.
This position is unattractive but, if true, it has the virtue of solving the problem by making identity over time impossible.
The ship is a new ship as soon as the 50%+1 threshold has been reached
After this 50%+1 threshold has been reach there is more new ship than old ship. To say the 1701 is still the 1701 after the 50%+1 threshold is to grant that identity to more of the ship that has not been present for the history of the ship than what was there from the start. So, this position appears a little more defensible than the first. However, there’s a catch. If the ship is to be replaced a piece at a time until 50%+1 replacement has been achieved, the 1701 will have to first have 50% of its parts replaced. If at 50% original/50% new parts the 1701 is still the 1701, we are in a similar same position as we were at the start of the previous claim – that as soon as one piece is changed the identity of the ship has changed. If we change any one part, the 1701 ceases to be itself and becomes a new ship. It doesn’t matter what part we replace, we will have a different ship.
Once all the parts of the ship have been replaced the ship is a new ship
The difference between the 1701 and the 1701-A is an example of a whole-hog approach. But what if Scotty and his crack team of engineers, over the course of years (maybe decades), replace the 1701’s parts one or a few at a time. A console breaks down, swap it out. A piece of transparent aluminum cracks, replace it. A nacelle gets shot off by an irate Klingon trader, get a new one. Until, over time, Scotty has replaced every single button, gyro, panel, self-sealing stem bolt, and piece of deck plating (some more than once). This process could take years, maybe decades. We might be comfortable saying the 1701 remains the same thing because the pieces had time to assimilate into the whole. The gradualness of the process does something to maintain identity. Exactly how long it takes a piece to properly acclimate to its new home is impossible to say, but we do accept this kind of continuity in other places. Our bodies are one, sports teams are another.
But what if … ?
Given that the process of the 1701 becoming the *1701* was called a refit, we can assume that we are looking at a piecemeal replacement of parts but that some of the 1701 remains in place and in use. Exactly what percentage of the 1701 was removed and replaced is unclear. However, given what we see on screen, I think it is safe to say that 50%+1 of the ship was replaced. So, we are assuming more than half was replaced but less than 100%. Are the 1701 and the *1701* the same ship in this case? If we believe it is a different ship, we are relying on the 50%+1 argument. If we believe it is the same ship, we are turning to the 100% replacement argument. Though neither of these arguments is beyond controversy, I did argue that the case for 100%-part replacement was stronger than the 50%+1 case. So, let’s say that after the refit the *1701* is still the 1701.
Fast forward slightly into the future. The Enterprise has saved Earth from V’ger but instead of next taking on Khan for a second time (an encounter that ends with the destruction of the 1701/*1701*) the Enterprise continues on for many, many years of service exploring deep space. During these years Scotty needs to make more and more repairs to the ship. And over time, all the parts have been replaced. Not one piece of the ship that was present when April, Pike or Kirk first sat in the captain’s chair remains. Is this ship still the 1701? If we are persuaded by the argument that once all the parts of the ship are replaced, we would say, no, it is not. The ship now being flown through the galaxy has no more in common with the 1701 than the 1701 had with any other ship made of completely different parts. Nothing of the ship remains, therefore there is no case to be made that it is the same thing.
That is, unless we find cause to consider the difference between the whole-hog and piecemeal approaches. It is not as if Khan forced Kirk to scuttle his ship and it was replaced by some new vessel called, I don’t know, the 1701-A. No. In this case the ship changes parts slowly, over time. It remained the same ship because as parts were replaced, they were conscripted, assimilated, or acclimated into the original whole. After all, you don’t become a different person if all of your matter is slowly replaced over time. If all your matter were dissipated at once, such that you ceased to exist and a copy were put in its place, that would be different. Even though nothing of the original ship remains, the means by which the ship came to such a state matters. The Enterprise 1701 is the same Enterprise post refit and post Scotty overhauls.
Scotty is a thrifty engineer. He threw away nothing. Scattered throughout the galaxy are all the old parts he replaced. A warp coil here, a phaser bank there. Scotty realizes that if he crisscrosses the galaxy, he has enough of the 1701 laying around that he can rebuild her! So, upon his retirement this is what he does. Scotty gathers all the discarded parts from the 1701 and puts them back together. She might not be pretty, she might barely be space worthy, but she’s all there. A Constitution class star ship made out of the discarded remains of the Enterprise 1701.
Which ship is the 1701? Is it the overhauled, refit, rebuilt vessel we’ve been calling the 1701 (despite not having any parts in common with the 1701 as it was coming out of space dock), or is it the “new” ship Scotty fashioned out of only parts from the 1701? They can’t both be the same ship any more than the 1701 can be a Klingon Bird-of-Prey. Again, arguments exist on both sides. If we place identity first and foremost on the parts that make up a thing, Scotty’s reconstructed 1701 would be the real 1701. But, before he put the scraps together, we were calling the ship made of replacement parts the 1701. Did identity somehow ‘transfer’ once Scotty’s ship came online? Doubtful, since nothing we have said about identity so far indicated that identity works in this way. Was it the case that the ship of replacement parts was never the 1701 in the first place? Possibly, but where was the 1701 when the parts were scattered all over the Sagittarius arm of the galaxy?
Identity is one of the thorniest problems that exists in philosophy. What makes this an especially frustrating problem is our need for identity of things. We want our stuff to be our stuff and be the same stuff today as it was yesterday. Despite our need for identity, an explanation of what identity consist of remains elusive. Maybe the Q can sort this one out for us.
 As is the case with the 1701-A and, presumably the 1701-B.
 … 1701 post refit and 1701-C.
 … 1701-D’s saucer section was destroyed, but the star drive section remained functional.
 Such is what happened when the USS Defiant NX-7402 was destroyed by the Breen (The Changing Face of Evil) and the Sao Paulo NCC-75633 was remained ‘Defiant’ (The Dogs of War).
 Our cells die and are replaced with regularity. The folk wisdom is that every seven years or so through this cellular replacement we have a whole new body. I’m not sure about the seven-year mark, but certainly our bodies undergo a slow change of material as time goes by.
 For example, the Detroit Cougars were founded in 1926. In 1930 they changed their name to the Falcons and in 1932 again to the Red Wings. Over the nearly 100-year history changes have not been limited to just the name. The player roster has turned over many times, they have called three different arenas home, and ownership has changed hands. Yet, through all of this we are comfortable with saying “The Detroit Red Wings” have continuously existed from 1926 to the present. (Don’t even get me started on the Cleveland Browns/Baltimore Ravens metaphysics fiasco).
7] For more on this issue please see the Philosopher’s Log post “Is the Transporter a Murder Machine: The Transporter, John Locke & Personal Identity”