Immaterialism and replacement

For the previous two Mondays, owing to the inspiration of Kagan's online Philosophy of Death lectures, I've written about a couple of problems with the physicalist notion of personal identity: resurrection and duplication. To summarize: resurrection is the reconstruction and revival of the body of a deceased person; duplication is the creation of a body identical to that of a living person. Both cases are similar in that they involve two identical copies of one body whereby the copies are made disjoint by a break in continuity. In the case of resurrection that break is in time by way of death; in the case of duplication that break is in space by way of replication. The problem each presents for physicalism is that, according to the physicalist notion that personal identity is purely corporeal, discontinuity shouldn't matter to personal identity. But according to common intuition about identity in general, as shown when we think about bikes and block towers being reassembled, discontinuity seems to matter.

I wrote about resurrection and duplication to lay the foundation for expressing my own view about personal identity—which, as I've already alluded to, is that common intuition is misguided. But before I move on to explaining myself, I want to address an objection many people would raise now, if not sooner: that physicalism is wrong from the start because it neglects the non-physical aspect of a person's existence—i.e., their soul.

Far be it for me to convince anyone who believes in immaterialism to change that belief. There's no bulletproof argument against the existence of souls for the same reasons there are no bulletproof arguments against the existence of anything that's unfalsifiable. I've written about that here. I'm not going to argue against the existence of souls—not in this post.

Instead, I'll point out that immaterialism leads to the same kinds of philosophical conundrums as physicalism does. In particular, theories about immaterial existence struggle with discontinuity, too. First of all, immaterialism also suffers from the problem of duplication: Supposing a soul is copied into a second body, do the two souls constitute the same person or two different persons? Just as with duplication as it pertains to physicalism (and the case of two William Rikers), the answer isn't clear.

Replacement

A problem that's unique to immaterialism is replacement. Replacement is the swapping out of one soul with another. For example, if Jones goes to sleep one night with a soul, X, but wakes up with a different soul, Y, then his soul has been replaced.

Replacement may sound implausible, but the problem isn't how likely replacement is to occur. Instead the problem is: how can you know if or when replacement occurs? In short, the answer is: you can't.

Because souls are immaterial, they are undetectable by direct observation. Instead, we observe souls only by indirect means, such as knowing a person's behavior, memories, and desires. If a soul is swapped out with a soul that produces the same behaviors, memories, desires, etc. as the first soul, then it's impossible to know replacement has occurred. To everyone outside that person, it will appear as though one soul has existed all along, undisturbed. Even to the person (or persons) of the replaced soul, the newly swapped-in soul could produce all the same qualia as the previous soul did, thus giving even Jones the himself the illusion that no replacement occurred.

I won't elaborate on the problem of replacement. Just as I'm not going to argue against the existence of souls, it's not my purpose to argue the merits of replacement as an objection to immaterialism. Instead, my point is that while many people may think immaterialism is immune to the kinds of problems of continuity that plague physicalism, both belief systems suffer their share of problems. It's that both systems suffer these problems that leads me to my view on personal identity, which I'll explain next Monday.