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Is there some philosophical basis for temporal coherence of our identity?

I noticed that there were many changes in my beliefs and personality throughout my life, e.g. me from 2000 probably would despise the political positions of the present me. Yet me from 2000 was doing many good things for the health of the present me (even if they were not always the most pleasant option such as eating healthy) and me from 2000 was sending me money (by saving his earnings). Why would he do that?

Also mechanical and chemical damage to the brain can change our personalities: make us irresponsible, or make us ignore the left part of the world, or make us forget all the memories up to some point, or make us incapable of forming new memories, or make up incapable of recognizing our spouses. Then the past and the future persons are fundamentally different. So why should the past person care about the future person?

I guess in evolutionary terms, a neurological system that cares about the future versions of itself is more likely to reproduce but is there some rational reason do that as well?

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    How do minor changes make a person "fundamentally" different? And perhaps time is an illusion that "keeps everything from happening all at once", so persons of now and then are really slices of a single spatiotemporal entity. Generally, "rational reasons" can not make it so that we should do anything at all, only values have such powers. All reasons can do is relate derivative values to the more fundamental ones. So what do you value, fundamentally, that moves you to do things? Because you can also choose not to care, and live in the moment as they say. Make that a value.
    – Conifold
    Sep 5, 2020 at 8:56
  • Don't concern yourself with the future, but still water your lemon tree, you planted yesterday. Over-thinking can do more harm than good. Sep 5, 2020 at 8:58
  • Why do you care about your family? Is the reason the same as why you care about your future self? (I don't know the answer to this question.)
    – N. Virgo
    Sep 6, 2020 at 2:43
  • @urmom: Why didn't you take a snoozing time or a small division of time (one second before and after) and consider as past and future and ask this question? Sep 6, 2020 at 15:51
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    In the title, I thought you were talking about your drunk hookup, not yourself. . . . Good Lord, I need Jesus. Sep 6, 2020 at 17:08

2 Answers 2

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This question raises a lot of interesting problems about the continuity of self and consciousness, but I think it can be cut down with a very pragmatic, down to earth approach.

Quite simply, the idea that the person we will be tomorrow is a different individual than the present us is contradicted by the fact that, so far in our life, we have the continuous experience of having to live with the consequences of our past actions.

Think about any decision you made that you regretted. I bet you experienced this regret and hardship first hand, subjectively, as happening to you, not to a third person. This feeling of regret, coupled with the memory of making the decision(s) that led to it, constitutes the experience that allows us to figure that, should we take a similar decision in the future, we will have to experience first hand the consequences, not some distant and abstract "future me".

Our experience tells us that if we party too hard on Saturday, we are hung over on Sunday. Whatever word game we can make up that "tomorrow's us is not us", the fact is that we, personally, in the first person, have to suffer through the headache and nausea. This is what we experience to be the case. It simply never happens that we party, and someone else has to go through our hangover.

As we grow older and gain experience, we are able to infer this pattern over longer time periods and more abstract problems, like saving money or keeping healthy. We know that if we don't save now, we, and no one else, will have to endure the state of being broke because of it. It is what our whole experience of life indicates.

Of course, this has to be mitigated with our desire to enjoy life here and now. It becomes a straightforward trade off: how much sacrifice now is worth avoiding trouble later. This is an emotional balance between our desire to enjoy now and our desire to avoid foreseeable trouble, directly conditioned by our ability to accurately forecast said future. (Concerning the balance of desires in the individual guiding our choices, see Spinoza's Ethics). Modern psychological studies tend to support the idea that our decisions are motivated by emotions first, and only then supported by a rational argument we make up for them.

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This question is related to the question of persistence in personal identity -- what makes a person at one time the same as a person at another time? Much has been written about that, including the question of whether major changes to a person such as the ones you describe cause it to no longer be the same person. If there is a fundamental sense in which, under some conditions, you stay the same person, then this might form the basis for why you should care about future you (more than about another future person). For that, it seems that more is necessary than just coming up with some convenient definition of what it means to be the same person. But there are some theories in metaphysics that would provide a basis for something like that, such as this recent paper. You may also enjoy this book: Time Biases: A Theory of Rational Planning and Personal Persistence, which addresses many of these issues.

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