Isaiah asked:

How well can we explain our personal identities? Consider identity at time, identity over time, and memory.

Answer by Caterina Pangallo

It is difficult to explain personal identity well!

We often speak of one’s personal identity as what makes one person one.

One basic concept of personal persistence over time is simply to have continuous bodily existence. This is irrespective of the fact that about every 10 years every cell in our body has been replaced.

This is called the ‘forensic’ identity. What this means is, that the law will take your body as your personal identity. E.g. if you commit a murder and then forget, you are still considered the murderer, if the evidence is conclusive.

But most of us agree with Locke, that personal identity is based on consciousness. We are the same person to the extent that we are conscious of our past and future thoughts and actions in the same way as we are conscious of our present thoughts and actions.

This is the philosophical position.

But now there is a problem. Suppose you go into a coma. When you awake all your memories are gone. This means you can have no consciousness of your older self any more.

This question has been asked many times by philosophers because they assume that every person is a person. And that nothing is in fact a person that could possible exist without being a person.

But I think there is a way around this.

Not having memories is a not an identity problem, but a problem of access.

It returns us to the forensic definition.

Every person’s experiences are laid down in their memories. When brains are disabled, their self-consciousness can cease, or it might change.

They may acquire new memories after trauma, without access to the old ones. Or they may, as sometimes happens, not be able to hold any memories at all.

There is a famous case of Phineas Gage, a man who lost his memory as well as the ability to remember from day to day.

He remained the personal identity, however.

People who knew him before knew he was the same person, but were of course compelled to acknowledge that he did not remember them. This included new acquaintances which he could not remember the next day.

So I think the solution to your question is:

1. Personal identity is tied to your body, which remains the same despite a complete turnover of all its cells every 10 years or so.

2. Personal identity is tied to your consciousness of self, which under normal circumstances remains with you until you die.

3. Personal identity is tied to your memories, which are always accessible in principle, even if you cannot remember some things when you try. (In any case, memories can change in quality as you get older).

Loss of body is impossible.
Loss of consciousness or loss of memories does not change or destroy personal identity as long as there are witnesses who can testify to the forensic identity of that person.

A person who is stranded on a desert island might have loss of identity and memory. But in this case you have to ask, what difference does it make?

Personal identity is essentially a social construct.

If there’s only one person in the world, the idea of identity is useless.

Same with the desert island person. If that person cannot make contact with persons elsewhere, then personal identity is a superfluous concept.