# Time Biases

Book review: Time Biases: A Theory of Rational Planning and Personal
Persistence, by Meghan Sullivan.

I was very unsure about whether this book would be worth reading, as it
could easily have been focused on complaints about behavior that experts
have long known are mistaken.

I was pleasantly surprised when it quickly got to some of the really
hard questions, and was thoughtful about what questions deserved
attention. I disagree with enough of Sullivan's premises that I have
significant disagreements with her conclusions. Yet her reasoning is
usually good enough that I'm unsure what to make of our disagreements -
they're typically due to differences of intuition that she admits are
controversial.

I had hoped for some discussion of ethics (e.g. what discount rate to
use in evaluating climate change), whereas the book focuses purely on
prudential rationality (i.e. what's rational for a self-interested
person). Still, the discussion of prudential rationality covers most of
the issues that make the ethical choices hard.

### Personal identity

A key issue is the nature of personal identity - does one's identity
change over time?

Sullivan starts this discussion by comparing a single-agent model to a
model with multiple distinct stages.

I initially found that part of the book confusing, as neither model
seems close to mine, and she seemed to present them as the only possible
models. Then somewhat later on in the book, I figured out that both
those models assumed that identity needed to stay constant for some
time, and that in the case of the multiple stage model, the change in
identity was discontinuous.

Sullivan prefers that kind of single-agent model, and therefore
concludes that we should adopt a time-neutral stance (i.e. she rejects
any time-discounting, and expects us to care as much about our distant
future selves as we care about our present selves).

Sullivan eventually compares that single-agent model to some models in
which a current self partially identifies with a future self, which
would allow for time-discounting of how much we care about a self.

The most interesting of those models involves some notion of
connectedness between current and future selves.

This feels like the obviously right approach to me. I expect it to work
something like the "me" of a decade ago or a decade in the future being
something I consider to be maybe 75% "me". I.e. I practice
time-discounting, but with a low enough discount rate that it might be
hard to distinguish from no discounting in many contexts.

Sullivan looks at some possible measures of connectedness, and convinces
me that they don't explain normal attitudes toward our future selves.

I suggest that she's too quick to give up on her search for
connectedness measures. I think the things which cause me to care about
my future self more resemble what causes me to feel connected to
friends, so it should include something like the extent to which we
expect to interact. That includes some measures of how much my present
self interacts with my future self. I don't have anything resembling a
complete model of how such connectedness would work, but I'm fairly
confident that people do use some sort of connectedness model for
deciding how much to identify with future selves.

Sullivan argues that concern-based discounting of future selves would
require changes in how we evaluate our age (e.g. if my two-year-old self
wasn't connected enough with my current self, then there's something
wrong with starting at birth to count my age). I agree that it implies
there's something imperfect about standard answers to "how old am I?",
but it seem perfectly reasonable to say we want easily checkable answers
to how old we are, even if that discards some relevant information.
("[All models are wrong, but some are
useful](https://en.wikipedia.org/wiki/All_models_are_wrong#Quotations_of_George_Box)").

If Sullivan can misunderstand our models of how old we are, then it's
easy to imagine that she's made a similar mistake with how much we
should care about existence over time - i.e. Sullivan sees that it's
useful to treat people as time-neutral for the purpose of, say, signing
contracts; whereas for other purposes (e.g. do people save enough for
retirement?), I see people caring less about their future selves. It
seems likely that time-neutrality is a good enough approximation for
most of our activities, which rarely require looking more than a decade
into the future. Yet that doesn't say much about how to model
substantially longer time periods.

It's more common for people to discount the future too much than too
little, so it's often wise to encourage the use of models with less
discounting. That creates some temptation to go all the way to zero
discounting, and doing so may be a good heuristic in some cases. But it
produces weird results that I mention below.

### Caring about the past

Sullivan devotes a substantial part of the book to arguing that it's
meaningful to have preferences about the past, and that rationality
prevents us from discounting the past.

An example: people who sue in response to an accident that caused them
pain will ask for more compensation if asked when they're in pain than
if they're asked when the pain is in the past.

Sullivan provides other examples in the form of weird thought
experiments about painful surgery followed by amnesia, where I might be
left uncertain about whether the pain is in my past or my future.

No one example seems convincing by itself, but there seems to be a real
pattern of something suspicious happening.

Sullivan convinced me that preferences about the past mean something,
and that there's something suspicious about discounting the past -
unless it follows the same discounting rules as apply to the future.

But I don't find it helpful to frame problems in terms of preferences
about the past. [Timeless decision
theory](https://wiki.lesswrong.com/wiki/Timeless_decision_theory) (TDT)
seems to provide a more natural and comprehensive solution to these
kinds of problems, and assumes time-neutrality, or a discount rate
that's low enough to approximate time-neutrality over the relevant time
periods. (I'm unsure whether TDT is understood much beyond the rather
specialized community that cares about it).

Sullivan's approach seems to leave her puzzled about [Kavka's toxin
puzzle](https://en.wikipedia.org/wiki/Kavka%27s_toxin_puzzle). It seems
that something in her premises implies that we can't become the kind of
person who follows TDT (i.e. follows through on a commitment to drink
the poison), but I haven't quite pinned down what premise(s) lead her
there, and it seems to leave her in a position that looks time-biased.
Specifically, she seems to imply that there's something irrational about
making a time-neutral decision to drink the poison. Yet in other parts
of the book, she says that our decisions shouldn't depend on what time
we happen to find ourselves located at, assuming all other evidence
available to us remains the same.

Sullivan is careful to distinguish care for the past from the sunk cost
fallacy. One relevant question is: did I get new info which would have
altered my prior self's decision? Another approach is to imagine what an
impartial observer would say - that helps make it irrelevant whether an
event is in my past or my future. I probably missed some important
nuance that Sullivan describes, but those seem like the important
distinctions to make.

### Afterlives

How should we think about really long lifespans?

Sullivan uses a strange (but harmless?) concept of afterlife, which
includes any time experienced after an "irreversible radical change",
e.g. heaven, dementia, or quadriplegia.

A key claim (which I'll abbreviate as SALE) is:

> **The Simple Approach for Life Extension:** it is rationally
> permissible (and perhaps rationally obligatory) to prefer some
> potential future state of affairs A over some potential future state
> of affairs B if A has greater aggregate expected well-being than B.

I reject the obligatory version of this claim, because I discount future
well-being. If I adopted the time-neutrality that Sullivan endorses, I'd
endorse the obligatory version of SALE.

Sullivan is uncomfortable with SALE, because it leads to the "single
life repugnant conclusion". I.e. that a sufficiently long life of
slightly positive well-being is better than a short life with more
well-being. She doesn't describe a good reason for a time-neutral person
to find this repugnant, so I'm inclined to guess that she (and most
people) find it repugnant due to a (possibly unconscious) preference for
time discounting.

My reluctance to endorse the single life repugnant conclusion seems to
be purely a function of my caring more about near-future versions of
myself than about distant-future versions.

Sullivan doesn't seem to identify anything repugnant about the
conclusion beyond the fact that it feels wrong. So I'm left guessing
that her intuitions of repugnance result from intuitions that distant
future selves are less important.

She can, of course, believe that those intuitions are irrational, and
that she's trying to overcome them. But then why doesn't she also try to
overcome the feelings of repugnance about the single life repugnant
conclusion?

Sullivan describes another version of SALE's consequences, asking us to
imagine that hell has enough breaks in the torture that it yields an
average positive balance of well-being, for eternity. It looks to me
like she's trying to prejudice our intuitions with words that suggest a
life that's worse than non-existence, and then contradicting that
impression when she gets more specific. I don't see what the substance
of her objection is here.

It seems my main disagreement with Sullivan boils down to the choice
between:

A\) agreeing that we will care less about distant future versions of
ourselves than near future versions (i.e. accept something like
time-discounting),

or

B\) running into repeated conflicts between our intuitions and our logic
when making decisions about time-distant versions of our selves.

Either choice appears to produce ordinary results when dealing with
relatively familiar time periods, and strange results when applied to
unusually long time periods. Choice A seems a bit simpler and clearer.

### Conclusion

The book is mostly clear and well-reasoned, with a few important
exceptions that I've noted, and those exceptions are about topics that
seem to confuse most philosophers who tackle them.

I expect that many people will learn something important from the book,
but it caused me to mostly just reinforce my existing beliefs.