Re: personal identity

Wei Dai (
Thu, 8 Jan 1998 18:10:07 -0800

On Thu, Jan 08, 1998 at 10:53:18AM -0800, Hal Finney wrote:
> I see a couple of problems. The first is a trivial matter of language.
> It is very confusing to write that A is B but B is not A. Normally we
> use the term "is" in a symmetrical way. It's not even clear which
> way to interpret a question like "are you the same person you were a
> second ago?". So you might want to use a different phrasing.

I don't think using "is" in an asymmetric way is necessarily confusing. We
handle sentences like "a penguin is a bird, but a bird is not necessarily
a penguin" without too much trouble. The reason I use "is" is that we
often hear questions like "is an upload of me really me?" from people who
have no clear idea of what "is" means in that context. I am suggesting
such a meaning.

> The larger problem is that this seems to over-emphasize the importance of
> memory. Our memories are important, but it seems to me that identity
> requires more than just remembering. If my mind were invaded tomorrow and
> rearranged so that my motivations, beliefs, and desires were completely
> different, then I would view the result as a different person even if it
> kept all my memories.

What if you read a book that is so persuasive that you change all of your
motivations, beliefs, and desires? Would you say the person who finishes
reading the book is no longer you? Is it really possible to completely
change someone's motivations, beliefs, and desires without touching his

> I also wonder about the gray areas. I don't remember most days of my
> life, so probably on most days I can expect that in the future I won't
> remember those days. This would seem to imply that after a few years
> I will no longer exist. Supposing I am offered the opportunity for an
> immortal lifespan, should I refuse it since I won't remember the present
> day after some years? That doesn't seem right.
> Maybe you should extend it so that you write A < B to indicate that B
> "is" A (e.g. remembers being A), and add as an axiom that A < B and B < C
> implies A < C. This way I stay alive as long as each day I remember the
> day before, even if after a while I have completely forgotten today.

I haven't decided whether this more liberal notion of identity is more
attractive. But as a practical matter, if you're offered immortality
today, you'd probably remember the day longer if you accepted than if you