Fusions and organisms

Suppose you believe the following:

1. For any physical objects, the xs, there is a physical object y with the following properties:
   1. each of the xs is a part of y;
   2. it is an essential property of y that it have the parts it does; and
   3. necessarily, if all the actual proper parts of y exist, then y exists as well.

For instance, on the standard version of mereological universalism, it seems we could just take y to be the fusion of the xs. And on some versions of monism, we could take y to be the cosmos.

But it seems (1) is false if organisms are physical objects and if particles survive ingestion. For suppose that there is exactly one x, Alice, who is a squirrel, and at t₁ we find a y that satisfies (1). And now suppose that at t₂ there comes into existence a nut whose simple parts are not already parts of y, and at t₃ this nut has been eaten and fully digested by Alice. Suppose no parts of y have ceased to exist between t₁ and t₃. Then y exists at t₃ by (c), and has Alice as a part of itself (by (a) and (b)), and the simple particles of the nut are parts of y by transitivity as they are parts of Alice. Hence y has gained parts, contrary to (b), a contradiction.

(Note that the argument can be run modally against a four-dimensionalist version of (1).)

The mereological universalist’s best bet may be to deny that fusions satisfy (c). Normally, we think that the only way for a fusion to perish is for one of its proper parts to perish. But there may be another way for a fusion to perish, namely by certain kinds of changes in the mereological structure of the fusion’s proper parts, and specifically by one of the fusion’s proper parts gaining a part that wasn’t already in the fusion.

Here is another problem for (1), though. Suppose that Alice the squirrel is the only physical object in the universe. Now consider a y satisfying (1)(a)–(b). Then y is distinct from Alice because y has different modal properties from Alice: Alice can survive annihilation of one of her claws while y cannot by (b). But this violates the Weak Supplementation mereological axiom, since all of y’s parts overlap Alice. So we cannot combine fusions as normally conceived of (since the normal conception of them includes classical mereology) with organisms.

A way out of both problems is to say that there are two different senses of parthood at issue: fusion-parthood and organic-parthood, and there is no transitivity across them. This is a serious ideological complication.

Causation and memory theories of personal identity

Unlike soul-based theories, the memory, brain and body theories of personal identity are subject to fusion cases. There are four options as to what happens when persons merge:

• Singleton: a specific person continues, but we don’t know which one

• Double Identity: there was only one person prior to the fusion, wholly present in two places at once

• Scattered: there was only one person prior to the fusion, half of whom was present in one location and half of whom was present in another

• End: fusion causes the person’s demise and the arising of a new person.

The problem with Singleton is that it supposes there is a fact about personal identity deeper than facts about memories, brain-continuity and body-continuity, which undercuts the motivation for the three theories of personal identity.

Double Identity and Scattered are weird. Moreover, it leads to absurdity. For whether you and I are now one person or two depends on whether we will in fact fuse in the future, and we have backwards counterfactuals like: “If you and I fuse, then we will have always been one person.” This is just wrong: facts about your being a different person from me should not depend on what will happen. And consider that if you and I decide to fuse, thereby ensuring that we have always been one person J, either bilocated or scattered, then J exists because of J’s decision to fuse. But an individual cannot exist because of a decision made by that very individual.

That leaves End. I think End may be a good move for brain and body theorists. But it’s not a good move for memory theorists. For by analogy, we will have to say that fission causes a person’s demise, too. But then it is possible to kill a person without any causal interaction. For suppose you are unconscious and undergoing brain surgery under Dr. Kowalska. Dr. Kowalska scans your brain to a hard drive as a backup. A malefactor steals the hard drive from her as well as a blank lab-grown brain. If the thief restores the data from the hard drive into the lab-grown brain, that will result in fission and thus death. But the thief’s restoring of the data into the blank brain is something that can happen without any causal interaction with you. Hence, the thief can kill you without causally interacting with you, which is absurd.

Hence both Double Identity and End have causality problems on the memory theory: Double Identity allows someone to be literally self-made and End allows for killing without causation. It may be that if one is less of a realist about causation, these problems are less, but since memory itself is a causal process, it may be that memory theories of personal identity don’t sit well with being less of a realist about causation.