By Mike Dorf
The great pre-Socratic philosopher Heraclitus stated the following problem, which has much engaged philosophers ever since: Theseus sets out in a wooden ship; over time, various planks wear out and are replaced by new planks; eventually, every plank comprising the ship has been replaced; is the resultant ship the same ship in which Theseus set out?
In the foregoing statement of the Ship of Theseus puzzle, the issue is simply semantic: The answer depends on what we mean by same. But to see the question as simply semantic is to miss what Heraclitus was doing in this puzzle. In a great many contexts, we think sameness a matter of underlying reality. The issue is acute in the philosophy of personal identity. Am I the same person today as I was yesterday? As I was when I was an infant? As I will be when I am an old man?
Or, consider a variant of the Ship of Theseus problem that appears in the philosophical literature. Suppose that as each of the original planks of the ship wears out, it is not simply discarded but set aside, and that after many years, someone reassembles them into their original pattern. Now we have the question of which ship is the real ship of Theseus: The reassembled planks or the ship gradually constructed one-at-a-time from new planks? This puzzle can also be dismissed as semantic, but taking it seriously may shed light on what we think about teleportation in the Star Trek fashion. When Kirk and Spock beam down to a planet, do they beam down or are they killed aboard the Enterprise, while replicants who think they are Kirk and Spock and who have their memories are created on the planet? Would your answer change if--by analogy to the modified Ship of Theseus example--the transporter doesn't actually vaporize Kirk and Spock on the Enterprise but simply copies them, transmitting the information about the arrangement of their atoms down to the planet? A reductionist view within the philosophical literature argues that even with respect to personal identity, these questions are semantic, but that is a contested view within philosophy, and so one needs an argument for dismissing the alternative views as confusing a semantic question for a metaphysical one.
And what has all this to do with law, you ask. Well, next week the Supreme Court hears oral argument in Lozman v. City of Riviera Beach, which poses the question of whether a houseboat--or a "floating residential structure", as the petitioner calls it--is a "vessel" as that term is defined in the federal Dictionary Act, thereby triggering admiralty jurisdiction and the substantive rules of law that go with it. Everyone agrees that a fully operational boat is a vessel and that a house on land is not a vessel. How much does one need to modify the house before it becomes a vessel?
As with the Ship of Theseus, so too with the Houseboat of Lozman, we can see how a house can be transformed from a house to a boat (and thus a vessel) one modification at a time, such that it starts off as a non-vessel and ends up becoming a vessel but that the dividing line between non-vessel-ness and vessel-ness will be stipulative. In this sense, the riddle of the Houseboat of Lozman closely resembles the Sorites Paradox (generally attributed to that great Greek paradox peddler, Eubulides of Miletus): You have a heap of sand; you remove a grain; you still have a heap; you repeat the process; eventually you have no sand left, and thus no heap of sand, but the removal of no single grain of sand clearly demarcates the heap/non-heap distinction.
For myself, I don't think that every version of every one of these puzzles is simply a semantic question. To my mind, Kirk and Spock are either really dead or really transported down to the planet. But most of the classic statements of the puzzles do strike me as simply pointing out the imprecision of our language.
That's true of legal language too--and the critical point I wish to make is that this remains true even if one decides to be a purposivist in matters of statutory interpretation. We can think that the question of whether Lozman's houseboat/floating-residential-structure is a vessel should turn on the purposes of admiralty jurisdiction. But even so, there will be borderline cases in light of those purposes. Indeed, one claim of anti-purposivist textualists is that resort to a statute's purpose leaves the judge considerable discretion.
Speaking of the textualist/purposivist debate, my latest Verdict column uses the Lozman case to shed light on the Hart/Fuller debate. After all, whether Lozman's houseboat/floating-residential-structure is a vessel is a kind of watery version of the much-mooted hypothetical no-vehicles-in-the-park ordinance.