Chisholm believes two objects, a and b, cannot be identical unless they have all the same parts in common (excluding persons). Chisholm’s solution to the paradox works by the machinery of 3-dimensionalism and mereological nihilism. Given that Chisholm characterizes ordinary objects such as tables and chairs as “logical fictions,” placing his ontology in the camp of mereological nihilism seems reasonable. Chisholm fundamentally denies that there is such a thing as The Ship of Theseus insofar as it pertains to our traditional notion of an object over time. Since the parts of the ship are constantly changing, even at the most microscopic level, new objects are constantly replacing old objects, and there is no persistence of a single ship over time. Our perception of a ship is what Chisholm terms entia successiva, whereby a continuous succession of changing objects gives the false impression of a single object’s persistence through time. Chisholm explains, …such things as the Ship of Theseus and indeed most familiar physical things are really ‘fictions’, or as we would say today, ‘logical constructions’. They are logical constructions upon things which cannot survive the loss of their parts.1 (277) Only through loose and popular claims of identity may we say the dining room chair on Monday is the same as the dining room chair on Tuesday. Here, loose and popular identity functions via similarity in properties. In other words, the loose and popular sense of identity, the “is” of predication, is what allows us to say ship T0 “is” ship T5000. Here, “is” predicates particular properties, essential properties, which lead our language to deceptively equate one object with another. Strictly and philosophically speaking, however, T0 cannot be equated with T5000 when using the “is” of identity, since the two objects represent objects with different parts. How does the perdurantist respond to Chisholm? The perdurantist would certainly deny the strict and philosophical identity claim between two different temporal parts. But moreover, the perdurantist would also deny a loose identity claim on the basis that two temporal parts are as distinct as a hand and a foot. I do not think this constitutes major clash between Chisholm and the perdurantist. On Chisholm’s account, two temporal parts may be said to be loosely identical if there is sufficient similarity in their parts. This merely accounts for our everyday perception and ontological inferences. The perdurantist may still reject this – though I think this leaves him in a weaker position as he is left to devise a new linguistic mechanism to account for our everyday derivation of identity and commonsense notions of existence.
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It is important, however, to note what is required to make the philosophical leap from Chisholm’s metaphysic to perdurantism. As noted, the key difference between the ontology of Chisholm and the perdurantist is that Chisholm believes that the Ship of Theseus is mere fiction, an abstraction of thought and language, whereas the 4-dimensionalist believes the Ship persists in virtue of its extension across time via temporal parts. Eternalism – the view that the past and future are as equally real as the present – and unrestricted composition – which holds that any instance in which parts come together a whole is formed – may bring us from Chisholm’s theory to perdurantism. In this way, the perdurantist would consider the 4D object made of T0 and T5000 and all its other temporal parts – call that 4D object T* (and let the 4D object made of T0 and B and all its other temporal parts be called B*). T* is literally and strictly self-identical, exists at different times, and so strictly and philosophically persists over time, enjoys identity over time. The way T* achieves this is by having some temporal part, Tn, that exists wholly and entirely at any one given time. Have we thus arrived at an answer to the Ship of Theseus paradox? The perdurantist and Chisholm would deny the strict, philosophical equating of T0 and T5000, and T0 and B, though for very different reasons. This allows us, without contradiction, to maintain the transitivity of identity. Espousing perdurantism over Chisholm’s ontology also allows us to respect the intuitive idea that objects survive replacement of parts through a series of temporal parts. But suppose Theseus returns and demands his ship; which is he to be given? Perdurantism and Chisholm both reduce this question to a matter of semantics. To determine the answer, we must invoke societal conventions, legality, etc. Perhaps the law states that whichever ship functions best, or contains the majority percentage of original material, is the Ship of Theseus. Yet this is not a matter of metaphysics. Note that this is not to say a result of perdurantism is that which ship is the Ship of Theseus is a matter of semantics. Since both T* and B* shared the same temporal parts of the original Ship before any planks were removed, both T* and B* lay equal claim to its title. The identity over time of an object is an objective fact, though some questions presuppose identity in such a way that they must accordingly be answered on the basis of non-metaphysical principles. And of course, given Chisholm’s ontology this is clearly a semantic question, as Theseus is demanding a ship that Chisholm does not believe metaphysically exists at all. Though perdurantism may ameliorate our qualms insofar as the identity of inanimate objects persists through time, I think the identity of persons is forced into an unsavory position. Let us imagine sometime in the future you undergo a cerebral hemi-
The Oculus: The Virginia Journal of Undergraduate Research