De Re Necessity Reconsidered

De Re Necessity Reconsidered

The necessity of origin is a beguiling thesis, instantly plausible. It sounds right. Queen Elizabeth II was necessarily born to her actual parents; in no possible world does she have different parents. If she exists in a world, so do her parents, dutifully giving rise to her. If she exists, those two people must have shagged her into existence. But we need to examine more carefully what the content of the claim is: what exactly do we mean by “parent”? The natural interpretation is that the person Elizabeth necessarily derives from the persons who actually produced her. Thus, we have the (interesting) thesis that persons necessarily arise from specific other persons. The origin of a particular person consists of a pair of other persons. However, this claim is demonstrably false, as we can see by considering brain transfer cases. Suppose Elizabeth’s parents had their brains replaced by other people’s brains so that the resulting person is not identical to the original person; then she would have been born to different persons yet still be Elizabeth (that person). She would have come from the same sperm and egg, but had different persons as parents. In that possible world her actual parents (quapersons) might never have existed, yet she would, because the same human bodies exist in that world and do their procreative thing. If my parents had been body-snatched a few weeks before I was conceived, I would still exist, even though the persons of Joseph and June would not be my parents (they had long gone before I was born). Result: persons don’t have persons as their necessary origins—no person necessarily originates in a particular pair of persons. There is no such de re metaphysical necessity linking persons with persons. It is not difficult to come up with variants on this sort of thought experiment—for example, cases in which your parents suffer such drastic psychological changes that they are no longer the same person as before. You still exist in a world in which this happens. The reason is obvious: the bodies of your parents still exist in these possible worlds. We can thus easily modify the thesis to accommodate these counterexamples: people necessarily come from the bodies they actually come from. I couldn’t have arisen from the bodies of my parents’ neighbors, say: that wouldn’t have been me, even if that individual looked and talked just like me. But isn’t that thesis in turn subject to the same kinds of counterexample? What if my parents’ reproductive apparatus had been grafted onto distinct human bodies and the same reproductive acts performed? I would still exist but from different bodies—those bodies would be performing the necessary acts. That is because it is the sperm and egg that really matter, not the body in which they happen to live.[1] So, we need to reformulate the thesis to register this fact: a given person necessarily arises form a particular combination of sperm and egg. Now we seem in the clear—but are we? What if the sperm and egg were replaced but the DNA left the same? We change the cellular vehicle but preserve the genetic passengers. Then we would have numerically the same DNA molecules but numerically distinct sperm and egg. Does that change the identity of the person that results? Apparently not: we just need to reformulate the thesis yet again—the person necessarily comes from a specific packet of DNA (the enclosing sperm and egg be hanged). This is a physical object admitting of the type-token distinction: I had to come from that token chunk of DNA—a distinct token of the same type would not be me (this person). A twin of me isn’t me. Are we now home free? Not quite: what if in a possible world a fragment of my actual DNA chunk has been chipped off? That wouldn’t be the same DNA chunk (aggregate) and yet I might still exist in that world. How much of the origin object can be lost before the person ceases to be? None of this is as straightforward as it seemed at first when the example of Queen Elizabeth II was paraded before us. The necessity of origin is murkier than we thought, with different implications for the metaphysics of persons; it is more recherche, more obscure. Though not simply false. It has an analytical depth that wasn’t immediately apparent. There is a fine structure to it. We might say that the correct thesis is that persons necessarily come from their micro-origins, not from macro human beings.

We can parallel the above discussion for tables and pieces of wood. It sounds right to say that this table necessarily came from a particular tree; any table looking like this table but coming from a different tree wouldn’t be this table. But that can’t be quite right once we take account of certain operations on trees, such as splicing. Suppose that in a possible world the piece of wood that composes this table had been spliced onto another tree not the one it is joined to in the actual world. Then the table would have come from a different tree but from the same piece of wood. Well and good, then let us restate the thesis to acknowledge this possibility: the table necessarily comes from that particular piece of wood, no matter what tree it belongs to across possible worlds. Does that imply that it must come from the same bunch of atoms? Couldn’t the same tree part have been composed of different atoms (like an animal body)? Sure, so let’s make that explicit—we don’t mean the table had to have been composed of the same atoms, though it does need to come from the same (atom-independent) piece of wood. Again, this is starting to lose some of its initial clarity as a modal claim, though perhaps it deepens the interest (it’s not the lump of matter that counts). And we still have questions about how much of the piece is necessary in order to get the specific table in question—how much can be chipped off or replaced. Surely it doesn’t have to be the whole piece. Could the table exist but be an inch shorter because the piece of wood didn’t stretch as far as the actual piece? Things are murkier than we thought, less clear-cut (as it were).

What about necessities of natural kind? Is a particular cat necessarily a cat—could it (that cat) have been a dog or a platypus? Again, intuition is strong: no way that cat (any cat) could have been of another animal kind—in no possible world is a cat an elephant! But careful thought starts to blur the picture. A cat could certainly have had different properties from its actual properties—properties of location, food intake, color, etc. A small genetic alteration could make it bigger or smaller, changed its eye color, influenced its furriness. Cats come in breeds, so could a given cat have been of a different breed? It depends how breeds are individuated and how extreme the differences are. It could certainly be somewhat different phenotypically and still the same cat, but could a Maine Coon be a Siamese? Now intuition begins to waver and struggle: we don’t know what to say. Could this oak tree have been a beech tree? Could an octopus be a shark? What if the octopus’ egg were subjected to radiation and its DNA arranged like that of a shark, developing accordingly? Would that creature be identical to the octopus that now exists but in a shark’s form? Hard to say. There seem to be all sorts of gradations and weird cases; modal intuition turns soft. What seemed obvious at first now seems obscure, even meaningless. We go from clarity to cloudiness, confidence to diffidence. This doesn’t mean there aren’t clear cases—a cat couldn’t be a clock (an ordinary wristwatch). There is no possible world in which your pet cat is a Rolex! But what kind of argument could settle the difficult cases? They seem irresoluble. What does this tell us about de re necessity? Possibly this: there is such a thing as the indeterminacy of essence. Meaning has been held to be indeterminate, and quantum behavior too, but perhaps also necessity de re. There is just no fact of the matter about certain modal questions; modal reality can’t make up its mind about these questions, try as it might. The metaphysics of modality is therefore subject to inherent indeterminacy. Essence is real, but it’s blurry. At first it seems quite sharp and clear, but on closer examination it starts to wobble and darken. Possible worlds are not as well defined as we thought; some hover on the border of possibility. Necessity is not limpid and crystalline, much as we would like it to be.

I will end where I began—with origin. Are there also necessities of termination? Is it true that a person could only end with a single terminal offshoot? Consider the corpse: it results from an antecedent living organism, often a person. It isn’t identical to the person: the person is no more but the dead body lingers. Nor are the sperm and egg identical to the person. A person’s life is bookended by non-persons: eggs and corpses. Could a given person have a different corpse in another possible world? In this world the corpse is a certain dead body; in another world could it be a numerically distinct dead body? I think not: that body could not have come from a different living body, and the living body could not have produced a different dead body (given that it did leave one). Death necessarily turns a living thing into a single dead thing, across all possible worlds. My corpse could not be the corpse of Sydney Sweeney, say. The “corpse-of” relation is rigid across possible worlds. That seems evident enough, as evident as the necessity of origin. True, we can manufacture hard cases: if the corpse is headless in a possible world, is it the same corpse as the one still joined to a head in the actual world? What if it loses even more of its parts? In any case, there is a symmetry between origin and terminus, modally speaking: both are subject to de re necessities. We should therefore add necessity of termination to necessity of origin.[2]

[1] I am obviously drawing on Kripke’s discussion of origin in Naming and Necessity, which in turn draws on a 1962 discussion by Timothy Sprigge. Kripke is well aware of the need to restrict the thesis to the sperm and egg, though he doesn’t mention the further possibilities I consider here. I take this for granted in my paper “On the Necessity of Origin” (1976).

[2] We can imagine reversing origin and terminus such that a person begins as a corpse and ends as a pair of cells. First, the dead body exists and life is breathed into it (think Frankenstein’s monster); then, at the end, the person’s body gradually withers away so that only a pair of cells remain. We could accordingly say that the person necessarily came from a certain corpse (lifeless body) and necessarily ended in a certain pair of cells. The table might likewise begin in a pile of ashes and end as part of a living tree (this would be a rather miraculous possible world).