Hume argued, not that there’s no self, exactly, but that there’s no substantial self.

I’m not entirely persuaded. Consider the following imaginary case:

You’re on a base on the Moon. The oxygen delivery system has malfunctioned and you’re suffocating to death. You step into a machine that scans everything about you down to the last detail, including all your neural pathways and hence all your memories, and transmits this information to Earth. On Earth, the information is used to produce an exact duplicate of you. The “you” on the Moon dies of oxygen deprivation, but the “you” on Earth goes on living. So who are you: the one who died on the Moon, or the one living on Earth?

It seems to me that there’s a duplicate of me on Earth, and that what’s left of the original me is on the Moon. Why? Because although the duplicate has all my memories and experiences and is just like me, I am not the subject of those experiences. My experiences are mine because they happened to me, not merely because they happened.

In other words, I am constituted as an ego, a self that has experiences and is not merely constituted by them. Now imagine a variant of the thought experiment:

Shortly after your information is transmitted to Earth and a duplicate of you is created, the oxygen system on the Moon starts working again and you recover. Now which one is you – did you survive on the Moon, or were you transmitted to Earth? Is neither of them you? Are the person on the Moon and the person on Earth both you?

If there were no substantial self, and if the self were nothing more than continuity of experience, wouldn’t we have to answer “both”? But that can’t be right: to be an individual is to be identical to oneself and nothing but oneself.

Although this is the way things look to me most of the time, there are days when Hume’s “bundle view” strikes me as more plausible. Derek Parfit, who came up with the thought experiments, believed that although the ego view seems plausible at first, the bundle view turns out to be right. And if the self consists in continuity of experience and nothing more, then all that’s unusual about the duplicate self is the causal mechanism responsible for the continuity.

What the imaginary cases show, Parfit thought, was that under sufficiently unusual circumstances there just is no fact of the matter concerning who is you. More importantly, he argued, it might not make much difference one way or the other.

Below, Louis Janet, The Flight of the Soul, 1854.