Persistence of Self-Identity Through Time

Should I be responsible for things I did ten years ago? Or am I a different person now than I was then? And not just in a ‘personal growth’ way, but actually a different person.

When I was younger, I did a lot of things that I now look back on and cringe over. The person I was ten years ago had a different decision-making process than what I have now. So, in what way can we say that myself from ten years ago (or fifteen or twenty) is numerically identical to me?

Physically speaking it’s not true. Cells die and new ones are born. The constituent atoms of cells are replaced through metabolic pathways. And I don’t even look the same as I did a decade ago – I’m older and (unfortunately) heavier. It’s a Ship of Theseus predicament:



Is it just memory that connects me? Because there is likely a lot of stuff I’ve forgotten since ten years ago. Does that mean I’m that same person to some lesser degree? Does that mean I’m not the same person as I was when I was a newborn infant, since I remember nothing from then? People still speak of me like newborn me was just me before I grew up.

If it’s not mental, is it genetic? I still have the same genetics I did ten years ago. But if I had an identical twin sibling that’d be true of him, too, and nobody would say that we’re the same person.

Is it a soul that keeps myself continuous with who I was in the past? Are all the sins of my past self stuck to my soul such that the present me has to carry them, despite not having the same decision-making temperament? Why should what I did ten, fifteen, twenty years ago stick with me today?

That brings up the crux of why this conversation isn’t just more philosophical navel-gazing. Just about every justice system in the world is predicated on the idea that a person maintains some essence or soul that persists through time. An eighteen year old commits a heinous murder and gets sentenced to life in prison: should they, at age sixty-five, be held responsible for what they did when they were eighteen? No matter how much they might have changed? What about if they sustain a serious head injury that gives them amnesia and they can’t even remember committing the crime?

The focus can be broader, too. Is there anything a person can do that’s seen as socially irredeemable? For instance, if you made a racist joke on Twitter ten years ago, and people find out about it now, should that affect whether you get that you’re interviewing for job tomorrow?

My view is that a person should only be held responsible for who they are now. Of course, who they are now is illustrated by past behavior, so it has to be taken into account. But I do think that people become, in a very literal sense, different people over time. On a physical level, what connects us to ourselves is the persistence of a neural pattern through time – who we are is dictated by a person’s signature connectome. To the extent that the particular connections in a person’s brain changes over time, the person becomes a different person.

This, of course, leads to some seemingly absurd sounding conclusions. If a person’s connectome was recorded at an instantaneous point in time and then instantiated in multiple other brains, are all those other brains literally the same person? What about Derek Parfit’s famous teleportation paradox thought experiments from his 1984 book Reasons and Persons?



Everyone, I think, has an intuitive sense of their own identity persisting through time. But I think if asked to look deeper at the issue, most people wouldn’t be able to explain what it means that they’re the same person they were yesterday and a decade ago. Derek Parfit essentially said that personal identity doesn’t matter.

I think he overlooks that intuitive sense of what it feels like to be me – that first-person, subjective, singular sense of ‘what it’s like to be Thomas Harper.’ I have first-hand knowledge of what that feeling was like while nobody else does. Even if I cringe about decisions I made ten years ago, I can still think about my internal state of mind from when I was making those decisions – I have access to the memory of having that first-person, subjective, singular experience.

But, wouldn’t the duplicate in Derek Parfit’s thought experiment also have access to those memories? What I think is different is that, even in remembering a past first-person, subjective, singular experience right now, that memory is seen through the lens of who I am right now. The memory takes on a new, different first-person, subjective, singular experience when I experience that memory as I am now. The duplicate, as soon as it gains consciousness, would immediately have it’s sense of what it’s like to be itself change, splitting off from the one left on earth. That would change its experience of remembering those memories, thereby changing its connection to them. That would make the duplicate a different person.

Something about this conception of identity still feels unsatisfying, but it’s the best I can come up with the explain it. Also, as a shameless plug, these ideas are something I play around with a lot in my Incarnate series, available on Amazon.