The scope of longtermism

The scope of longtermism
David Thorstad (Global Priorities Institute)
Global Priorities Institute | June 2021
GPI Working Paper No . 6-2021

The scope of longtermism
Abstract
Longtermism is the thesis that in a large class of decision situations, the best thing we can
do is what is best for the long-term future. The scope question for longtermism asks: how
large is the class of decision situations for which longtermism holds? In this paper,
I suggest that the scope of longtermism may be narrower than many longtermists
suppose. I identify a restricted version of longtermism: swamping axiological strong
longtermism (swamping ASL). I identify three scope-limiting factors — probabilistic and
decision-theoretic phenomena which, when present, tend to reduce the prospects for
swamping ASL. I argue that these scope-limiting factors are often present in human
decision problems, then use two case studies from recent discussions of longtermism
to show how the scope-limiting factors lead to a restricted, if perhaps nonempty, scope
for swamping ASL.
1 Introduction
If we play our cards right, the future of humanity will be vast and ﬂourishing. The earth
will be habitable for at least another billion years. During that time, we may travel well
beyond the earth to settle distant planets. And increases in technology may allow us to
live richer, longer and fuller lives than many of us enjoy today.
If we play our cards wrong, the future may be short or brutal. Already as a species
we have acquired the capacity to make ourselves extinct, and many authors put forward
alarmingly high estimates of our probability of doing so (Bostrom 2002; Leslie 1996; Ord
2020). Even if we survive long into the future, technological advances may be used to
breed su ering and oppression on an unimaginable scale (Sotala and Gloor 2017; Torres
2018).
Some authors have taken these considerations to motivate longtermism : roughly, the
thesis that in a large class of decision situations, the best thing we can do is what is
best for the long-term future (Beckstead 2013; Greaves and MacAskill 2021; Greaves et al.
forthcoming; MacAskill 2022; Ord 2020). The scope question for longtermism asks: how
large is the class of decision situations for which longtermism holds?
1
Longtermism was originally developed to describe the decisions facing present-day
philanthropists. Longtermists suggest that the best thing philanthropists can do today
is to safeguard the long-term future. But many have held that the scope of longtermism
extends considerably further. Hilary Greaves and Will MacAskill (2021) suggest that
longtermism holds in all of the most important decisions facing humanity today. Nick
Beckstead (2013) and Andreas Mogensen (2021) suggest that longtermism extends into
global health decisionmaking. And Owen Cotton-Barratt (2021) suggests that even most
mundane decisions, such as selecting topics for dinner-table conversation, should be made
to promote proxy goals which track far-future value.
In this paper, I argue that the scope of longtermism may be narrower than many
longtermists suppose. Section 2 clariﬁes my target: ex ante , swamping axiological strong
longtermism (swamping ASL). Section 3 illustrates a historical decision problem in which
swamping ASL may have been true. However, Sections 4-6 develop three scope-limiting
factors: probabilistic and decision-theoretic phenomena which, when present, tend to
reduce the prospects for swamping ASL. I argue that these scope-limiting factors are
present in many human decision problems. Sections 7-8 use a pair of case studies to show
how the presence of these scope-limiting factors leads to a limited, but perhaps nonempty,
scope for swamping ASL. Section 9 concludes.
2 Preliminaries
2.1 Longtermism: axiological and ex ante
Longtermism comes in both axiological and deontic varieties. Roughly speaking, axio-
logical longtermism says that the best options available to us are often near-best for the
long-term future, and deontic longtermism says that we often should take some such op-
tion. Longtermists standardly begin by arguing for axiological longtermism, then arguing
that axiological longtermism implies deontic longtermism across a wide range of deon-
tic assumptions. In order to avoid complications associated with the passage between
2
axiological and deontic claims, I focus on axiological rather than deontic longtermism.
Axiological longtermism can be construed as an ex ante claim about the values which
options have from an ex ante perspective, or as an ex post claim about the value that options
will in fact produce. It is generally thought that ex post longtermism is more plausible than
ex ante longtermism, since many of our actions may in fact make a strong di erence to the
course of human history, even if we are not able to foresee what that di erence will be.1
For this reason, most scholarly attention has focused on ex ante versions of longtermism,
and I follow this trend here.
The best-known view in this area is what has been called axiological strong longter-
mism (ASL):
(ASL) In a wide class of decision situations, the option that is ex ante best is
contained in a fairly small subset of options whose ex ante eects on the very
long-run future are best.2
My target in this paper will be a restricted form of ASL.
2.2 Swamping axiological strong longtermism
Let a longtermist option be an option whose ex ante eects on the very long-run future are
near-best.3ASL holds whenever the ex ante best option is a longtermist option. This can
happen in two ways.
1However, Section 4 and on some views also Section 6 will place limits on the scope of ex post longter-
mism.
2This is the form of longtermism considered in Greaves and MacAskill (2019). Greaves and MacAskill
(2021) defend a scope-restricted version of ASL, focusing only on the most important decision situations
facing humanity today. I use the older, more general formulation of ASL in order to avoid ruling out wider
scopes for ASL, and indeed Greaves and MacAskill are sympathetic to the idea that ASL has fairly wide
scope.
3More formally, suppose that value is temporally separable, so that Vo=So+Lowhere Vo;So;Loare
the overall, short-term and long-term values of option o. Assess changes in value Vo;So;Lorelative
to a baseline, such as the e ects of inaction. And take an expectational construal of ex ante value. Then a
longtermist option is such that E[Lo]Tmax o02OE[Lo0] whereOare the options available to the actor and
Tis a context-independent threshold for e ects that count as ‘near-best’. Perhaps we might take T=0:9.
3
First, let a swamping option be an option whose expected long-term beneﬁts exceed in
magnitude the expected short-term e ects produced by any option.4I call these swamp-
ing options because their long-term e ects begin to swamp short-term considerations in
determining ex ante value. The ﬁrst way for ASL to be true is if the best option is both a
longtermist option and a swamping option.
Swamping axiological strong longtermism (Swamping ASL) In a wide class
of decision situations, the option that is ex ante best is a swamping longtermist
option.
My focus in this paper will be on swamping ASL.
Second, the best option may be a non-swamping longtermist option , an option whose
expected long-term e ects are near-best, but do not exceed in magnitude the expected
short-term e ects of all other options. One way to defend the value of non-swamping
longtermist options would be through the convergence thesis that what is best for the
short-term is often near-best for the long-term as well.5The convergence thesis suggests
that even when long-term e ects do not swamp short-term e ects in magnitude, the best
option may nonetheless be a longtermist option, since the best short-term option will often
be near-best for the long-term.
I focus on swamping ASL for three reasons. First, swamping ASL ﬁgures in leading
philosophical arguments for ASL and in most nonphilosophical treatments of longter-
mism. Second, swamping ASL is the most distinct and revisionary form of ASL, because
it tells us that the short-termist options we might have assumed to be best are in fact
often not best.6Third, swamping ASL underlies many of the most persuasive arguments
4Using the notation and assumptions of the previous footnote, a swamping longtermist option is such
that E[Lo]>max o02OjE[So0]jwhereOare the options available to the actor. This is a simpliﬁcation of the
model from Greaves and MacAskill (2019).
5For example, you might think that the best thing we can do to ensure a good future is to promote
economic growth (Cowen 2018), and that is also among the best things we can do for the short-term. Note,
however, that this may be an example of a swamping longtermist option.
6Strictly speaking, this does not follow from swamping ASL since swamping ASL is compatible with
the convergence thesis. However, in practice most of the examples used to support swamping ASL are not
near-best in their short-term e ects.
4
from axiological to deontic longtermism, which rely on the claim that su ciently strong
duties to promote impartial value may trump competing nonconsequentialist duties. As
we move away from swamping longtermism, obligations to promote long-term value will
diminish in strength, putting pressure against the inference from axiological to deontic
longtermism.
2.3 Scope-limiting phenomena
In this paper, I illustrate three scope-limiting phenomena . These are probabilistic and
decision-theoretic phenomena which, when present in a decision problem, tend to re-
duce the prospects for swamping ASL to hold in that problem. Sections 4-6 introduce the
scope-limiting phenomena that will concern me: rapid diminution (Section 4); washing
out (Section 5); and option unawareness (Section 6). I argue that each scope-limiting
phenomenon is often present in the decisions that we face, then show how the presence
of each phenomenon reduces the prospects for swamping ASL.
To say that these scope-limiting phenomena reduce the prospects for swamping ASL
is not to say that the swamping ASL has empty scope. Section 3 illustrates a case in
which swamping ASL may well have been true, and Section 7 argues that this case is
not signiﬁcantly a icted by any of the scope-limiting phenomena. Moreover, it is not
impossible for swamping ASL to hold in some cases where all of the scope-limiting
phenomena obtain. However, the presence of these scope-limiting phenomena does put
pressure on many cases in which swamping ASL has been claimed to obtain. Section 8
illustrates one case of this type.
Summing up, my target in this paper is ex ante , swamping axiological strong longter-
mism. I illustrate three scope-limiting phenomena to suggest that swamping ASL has
more limited scope than we might otherwise suppose. But ﬁrst, let us consider where
swamping ASL may be plausible.
5
3 Swamping ASL and the Space Guard Survey
A popular way to motivate swamping ASL is to think about risks of human extinction
(Bostrom 2013; Greaves and MacAskill 2021; Ord 2020). Now on some views, the con-
tinued survival of humanity may have indi erent, or even negative value (Benatar 2006).
Given our potential to spread death and su ering, the universe may be better o once it
is rid of humanity. On these views, risks of human extinction will not motivate swamp-
ing ASL. But many philosophers are cautiously optimistic that the survival of humanity
would be a good thing (Beckstead 2013; Ord 2020; Parﬁt 2011). On these views, it may
be very important to protect humanity from premature extinction. And in some cases,
decisions to mitigate extinction risk may motivate swamping ASL.
One way that humans might go extinct is through the impact of a large asteroid on
earth. Indeed, there is mounting evidence that an asteroid impact during the Cretaceous
period killed every land-dwelling vertebrate with mass over ﬁve kilograms (Alvarez et al.
1980; Schulte et al. 2010). As recently as 2019, an asteroid 100 meters in diameter passed
ﬁve times closer to the earth than the average orbital distance of the moon and was
detected only a day before it arrived (Zambrano-Marin et al. 2021).
NASA classiﬁes asteroids with diameter greater than 1 kilometer as catastrophic, ca-
pable of causing a global calamity or even mass-extinction. Our best estimates suggest
that such impacts occur on earth about once in every 6,000 centuries (Stokes et al. 2017).
Plausibly, it is worth our while to detect and prepare for such events.
As evidence mounted of the threat posed by asteroid impacts, the United States
Congress funded the Space Guard Survey, a collection of projects aimed at tracking poten-
tially dangerous asteroids, comets and other near-earth objects. Since the 1990s, the Space
Guard Survey has mapped approximately 95% of the near-earth asteroids with diameters
exceeding 1 kilometer, at a cost of $70 million. From an ex ante perspective, how valuable
was the Space Guard Survey?
Let us work with a set of conservative assumptions, so we cannot be accused of
6
rigging the numbers. Assume ﬁrst that the Space Guard Survey can only accurately
predict impacts during the next century. Next, suppose that if an undetected asteroid
with diameter greater than 1 kilometer were to strike earth during the next century,
the chance of extinction would be one in a million. Now, consider that estimates of
the expected number of future humanlike lives range from about 1013to 1055(Bostrom
2014; Newberry 2021). This puts the Space Guard Survey’s expected cost of detecting
an extinction-causing asteroid impact, counting only impacts within the next century, at
about $7 per expected future life, and fractions of a penny using anything but the most
conservative estimate of future lives.7For comparison, our best estimates put the cost
of saving a life through short-termist interventions at several thousand dollars (GiveWell
2021), far exceeding the cost of the Space Guard Survey if we have any conﬁdence at all
in our ability to prepare for and survive an otherwise-catastrophic impact with su cient
warning.
Now consider the decision facing Congress in the early 1990s: whether to fund the
Space Guard Survey or to redirect the money towards alternative programs. Suppose,
plausibly, that the expected long-term e ects of the Space Guard Survey were near-best
out of all programs available for Congress to fund. Or, if this is not plausible, replace
the Space Guard Survey with any program that had near-best expected long-term e ects
and repeat the argument. Then suppose we also grant that the expected long-term e ects
of the Space Guard Survey exceeded in magnitude the best-achievable short-term e ects
of any competing program. For example, we might benchmark the long-term e ects of
the Space Guard Survey at several dollars per life saved, and the best-achievable short-
term e ects of competing programs at several thousand dollars per life saved. If this is
right, then swamping ASL was true of Congress’s decision problem. Funding the Space
Guard Survey was the best thing that Congress could have done; its long-term e ects
were near-best, and they swamped in magnitude the expected short-term e ects of all
7This estimate is arrived at by multiplying the expected number of future lives by the per-century
probability of a catastrophic asteroid impacting earth, as well as by the probability that an undetected
catastrophic asteroid impact would lead to extinction, then dividing the result by the program cost.
7
options. Indeed, it may be precisely on these grounds that Congress decided to fund the
Space Guard Survey.
Some readers might disagree with the claim that swamping ASL holds of Congress’s
decision problem. Perhaps you hold a person-a ecting axiology on which it is neither
good nor bad to ensure that future humans come into existence. Or perhaps you think that
the likely outcome of asteroid detection research is research into dangerous technologies
for asteroid deﬂection, and that the dangers posed by these technologies are greater than
the dangers they eliminate (Ord 2020). But in this paper, I want to emphasize a di erent
line of resistance: cases such as the Space Guard Survey are quite special (Section 7), in that
they avoid a number of scope-limiting phenomena (Sections 4-6) that serve to reduce the
prospects for swamping ASL. This means that we can, and perhaps should, acknowledge
some cases in which swamping ASL holds, while resisting swamping ASL as a description
of many other decision problems.
4 Rapid diminution
In the next three sections, I illustrate a series of scope-limiting factors. I argue that these
factors are often present in the decisions that we face and that, when present, these factors
tend to reduce the prospects for swamping ASL.
The ﬁrst scope-limiting factor is rapid diminution . Fix an option oand consider the
probability distribution over long-term impacts of o.8In most cases, the probabilities of
long-term impacts decrease as those impacts increase in magnitude. If probabilities of
impacts decrease more slowly than the magnitudes of those impacts increase, then the
expected long-term consequences of omay be astronomically high. But if the probabilities
of large impacts decrease quickly, the expected long-term impacts of omay be quite
modest.
Rapid diminution is a familiar feature of many of the best-known probability distri-
8I.e. consider the probability distribution over the partition f[L=k] :k2Rg.
8
butions. For example, suppose that we model the expected long-term impact of ousing a
normal distribution, centered around the origin, with a standard deviation equivalent to
the value of ten lives saved. On this model, the probability of long-term impacts exceeding
ﬁve times this value is less than one in a million. And the probabilities of astronomical
long-term impacts, while nonzero, will be so negligible as to have no signiﬁcant impact
on the expected long-term impact of o.
The argument from rapid diminution claims that many options exhibit rapid diminu-
tion in the probability of long-term impacts, limiting the contribution that long-term
impacts can make to the expected value of those options. This argument is supported by
persistence skepticism : the view that many of our actions do not make a large persisting
impact on the long-term future.
We can assess the case for persistence skepticism by looking at the burgeoning aca-
demic ﬁeld of persistence studies, which studies examples of persistent long-term changes
(Alesina and Giuliano 2015; Nunn 2020). Persistence studies often returns surprising neg-
ative results, where e ects that we might have expected to persist for a long time evaporate
after several decades. For example, given the scale of American bombing in Japan and
Vietnam, one might expect persistent economic e ects in the heaviest-hit areas. Given
the number of people a ected and the magnitude of potential e ects, this is exactly the
type of persistent e ect that would interest a longtermist. But a half-century later, there
are no statistically signiﬁcant di erences between the most- and least-a ected areas on
standard economic indicators such as population size, poverty rates and consumption
patterns (Davis and Weinstein 2008; Miguel and Roland 2011). For a striking example,
the cities of Hiroshima and Nagasaki returned to their pre-war population levels by the
mid-1950s.
Now it is true that persistence studies has identiﬁed a few-dozen e ects which might
be more persistent. For example, the introduction of the plough may have a ected fertility
norms and increased the gendered division of labor (Alesina et al. 2011, 2013); the African
slave trade may have stably reduced social trust and economic indicators in the hardest-
9
hit regions (Nunn 2008; Nunn and Wantchekon 2011); and the Catholic Church may be
responsible for the spread of so-called WEIRD personality traits identiﬁed by comparative
psychologists (Schulz et al. 2019). However, these ﬁndings need to be taken with three
grains of salt.
First, many of these ﬁndings are controversial, and alternative explanations have been
proposed (Kelly 2019; Sevilla 2021). Second, these ﬁndings are few and far between, so
together with other negative ﬁndings they may not challenge the underlying rarity of
strong long-term e ects. And ﬁnally, most of the examples in this literature also involve
short-term e ects of comparable importance to their claimed long-term e ects. Hence
the persistence literature may not provide strong support for the swamping longtermist’s
hope that persistent long-term e ects could swamp short-term e ects in importance.
At the same time, there is no doubt that some actions have a nontrivial probability of
making persistent changes to the value of the future far greater than any of their short-term
eects. As a result, we cannot get by with the argument from rapid diminution alone. We
need to supplement rapid diminution with a second scope-limiting factor: washing out.
5 Washing out
A second scope-limiting factor is washing out . Although many options have nontrivial
probabilities of making positive impacts on the future, they also have nontrivial prob-
abilities of making negative impacts. For example, by driving down the road I might
crash into the otherwise-founder of a world government, but I might also crash into her
chief opponent. As a result, the argument from washing out holds that there will often be
signiﬁcant cancellation between possible positive and negative e ects in determining the
expected values of options.
There are two related ways that the argument from washing out can be articulated. The
ﬁrst begins with the popular Bayesian idea that complete ignorance about the long-term
value of an option should be represented by a symmetric prior distribution over possible
10
long-term values. Next, the argument notes that we are often in a situation of evidential
paucity : although we have some new evidence bearing on long-term values, often our
evidence is quite weak and undiagnostic. As a result, the prior distribution will exert a
signiﬁcant inﬂuence on the shape of our current credences, so if the prior is symmetric
then our current credences should be fairly symmetric as well. And a near-symmetric
probability distribution over long-term impacts gives signiﬁcant cancellation when we
take expected values.
We can make a similar point by arguing for forecasting pessimism , the view that it is
often very di cult to predict the impact of our actions on far-future value. For example,
there is no doubt that the Roman sacking of Carthage had a major impact on our lives
today, by cementing the Roman empire and changing the course of Western civilization.
But even today, let alone with evidence available at the time, it is very di cult to say
whether that impact was for good or for ill.
Forecasting pessimism generates a type of washing out between possible positive and
negative forecasts.9When we make forecasts based on sparse data, we need to take
account of the fact that the data we have been dealt is a noisy reﬂection of the underlying
reality. As phenomena become more unpredictable and our data becomes increasingly
sparse, we should grow more willing to chalk up any apparent directionality in our
forecasts to noisiness in the hand of data that nature has dealt us. In other words, as
forecasting becomes more di cult we get increasing wash-out between possible positive
and negative forecasts that we could have made had nature dealt us di erent samples of
data.
Why should we be pessimistic about our ability to forecast long-run value? Intuitions
about the sacking of Carthage are well and good, but it would be nice to have some
concrete theoretical considerations on the table. Here are three reasons to think that we
are often in a poor position to forecast long-run value.
9Among the many ways to give formal expression to this idea, Gabaix and Laibson’s (2021) as-if
discounting brings out the similarity to the argument from evidential paucity by highlighting the role of
priors.
11
First, we have limited and mixed track records of making long-term value forecasts.
We do not often make forecasts even on a modest timeline of 20-30 years, and as a result
there are only a few studies assessing our track record at this timescale.10These studies
give a mixed picture of our track record at predicting the moderately-far future: in some
areas our predictions are reasonably accurate, whereas in others they are not. But the
longtermist is interested in predictions at a timescale of centuries or millennia. We have
made and tested so few predictions at these time scales that I am aware of no studies
which assess our track record at this timescale outside of highly circumscribed scientiﬁc
domains, and if our moderate-future track record is any indication, our accuracy may
decline quite rapidly this far into the future.
Second, there is an enormous amount of practitioner skepticism on behalf of prominent
academic and non-academic forecasters about the possibility of making forecasts on a
timescale of centuries, particularly when we are interested in forecasting rare events,
as longtermists often are. Very few economists, risk analysts, and other experts are
willing to make such predictions, citing the unavailability of data, a lack of relevant
theoretical models, and the inherent unpredictability of underlying systems (Freedman
1981; Goodwin and Wright 2010; Makridakis and Taleb 2009). And when risk analysts are
asked to consult on the management of very long-term risks, they increasingly apply a
variety of non-forecasting methods which enumerate and manage possible risks without
any attempt to forecast their likelihood (Marchau et al. 2019; Ranger et al. 2013). If
leading practitioners are unwilling to make forecasts on this timescale and increasingly
suggest that we should act without forecasting, this is some evidence that the underlying
phenomena may be too unforeseeable to e ectively forecast.
Third, value is multidimensional . The value of a time-slice in human history is de-
termined by many factors such as the number of people living, their health, longevity,
education, and social inclusion. It is often relatively tractable to predict a single quantity,
10For domain-speciﬁc track records see Albright (2002); Kott and Perconti (2018); Parente and Anderson-
Parente (2011); Risi et al. (2019) and Yusuf (2009). For discussion see Fye et al. (2013) and Mullins (2018).
12
such as the number of malaria deaths that will be directly prevented by a program of
distributing bed nets. And when we assess the track records of past predictions, we often
assess predictions of this form. But the longtermist is interested in predicting value itself,
which turns on many di erent quantities. This is harder to predict: distributing bed nets
also a ects factors such as population size, economic growth, and government provision
of social services (Deaton 2015). So even if we think that the long-term e ects of a program
along a single dimension of value are fairly predictable, we may think that the ultimate
value of the intervention is much less predictable.
Summing up, the argument from washing out claims that we often get signiﬁcant
cancellation between possible positive and negative e ects of an intervention when taking
expected values. One window into washing out comes from evidential paucity: because
we have little evidence about long-term impacts, we should adopt a fairly-symmetric
probability distribution over possible long-term impacts. The same phenomenon occurs
in thinking about forecasting. Because our evidence about far-future value is sparse, we
should think that our forecasts could easily have been di erent if we had received di erent
evidence about the future, and as a result we get signiﬁcant cancellation between possible
positive and negative forecasts of far-future value.
Together, rapid diminution and washing out put pressure on the scope of swamping
ASL. They do this by suggesting that the expected far-future beneﬁts of many options may
be relatively modest, and may be signiﬁcantly cancelled by the expected far-future costs
of these options. In the next section, I illustrate a third and ﬁnal scope-limiting factor:
option unawareness.
6 Option unawareness
Rational ex ante choice involves taking the ex ante best option from the options available
to you. But which options are these? We might take a highly unconstrained reading on
which any option that is physically possible to perform belongs to your choice set. But in
13
practice, this reading seems to betray the ex ante perspective (Hedden 2012).
Suppose you are being chased down an alleyway by masked assailants. A dead end
approaches. Should you turn right, turn left, or stop and ﬁght? Trick question! I forgot
to mention that you see a weak ventilation pipe which, if opened, would spray your
attackers with hot steam. That’s better than running or ﬁghting. Let us suppose that, in
theory, all of this could be inferred with high probability from your knowledge of physics
together with your present perceptual evidence, but you haven’t considered it. Does this
mean that you would act wrongly by doing anything except breaking the pipe?
Many decision theorists have thought you would not act wrongly here. Just as ex ante
choosers have limited information about the values of options, so too they have limited
awareness of the many di erent options in principle available to them. Theories of option
unawareness incorporate this element of ex ante choice by restricting choice sets to options
which an agent is, in some sense, relevantly aware of (Bradley 2017; Karni and Vierø 2013;
Steele and Stef ´ansson 2021). In the present case, this means that your options are ﬁrst
described: turning right, turning left, or stopping to ﬁght. Unless, perhaps, you happen
to be James Bond.
How is option awareness relevant to swamping ASL? To see the relevance, note that
rapid diminution and washing out are features of options, not decision problems. To-
gether, rapid diminution and washing out imply that many of the options we face will not
be swamping longtermist options, because their expected far-future beneﬁts may be rela-
tively modest and may be signiﬁcantly cancelled by expected far-future costs. However,
swamping ASL is a thesis about decision problems, which present us with a set of options
rather than a single option. Swamping ASL holds in any decision problem for which the
ex ante best option is a swamping longtermist option. The presence of a single swamping
longtermist option in a decision problem may be enough to vindicate swamping ASL.
This means that the number of options present in a decision problem bears strongly
on the likelihood that swamping ASL will be true in that problem. If the vast majority of
options are not swamping longtermist options, then swamping ASL will be unlikely to
14
hold in decision problems containing a dozen options, since it is unlikely that any of these
will be swamping longtermist options. But swamping ASL may be more likely to hold in
decision problems containing millions or billions of options, simply because one of those
options is likely to be a swamping longtermist option, and because swamping longtermist
options are often, when present, the best options we can take.11Hence swamping ASL
may be relatively plausible before we restrict agents’ option sets to incorporate their
limited awareness of available options, but less plausible once option unawareness is
incorporated.
To see the point in context, consider interventions aimed at combatting childhood
blindness. Nick Beckstead (2013) has suggested that the short-term beneﬁts of these
interventions, namely preventing children from going blind, may be swamped by the
long-term beneﬁts of preventing blindness, such as speeding up a nation’s economic
development or changing the world’s trajectory by changing the role that children will
play in the national and global economy. Our discussion of rapid diminution and washing
out suggests that, for most particular children, Beckstead’s claim will be false. Because it is
hard for a single individual to make a lasting impact on the long-term future, and because
individuals may also make negative impacts on the long-term future, for most children,
the expected beneﬁt of preventing them from going blind will be driven primarily by
short-term considerations, such as the value of not being blind.
However, perhaps it is not implausible that somewhere in the world, there is a col-
lection of seventeen children and a sequence of days such that, if each child were given
preventative treatment on the requisite day, the long-term trajectory of the world would
be signiﬁcantly improved. Let Obe the option of giving just this course of treatment
to each of the children in question. And perhaps it is not unreasonable to suppose that,
11As always, there is a problem of option individuation, since it is often possible to chop a single option
into millions or billions of nearly-identical options, but that is unlikely to improve the prospects of swamping
ASL. Readers are invited to approach this discussion in a way that treats awareness of relevantly di erent
options as raising the prospects for swamping ASL to be true. Like most philosophers, I do not pretend to
be in possession of a formal criterion for relevant di erence, or another fully formal solution to the problems
induced by option individuation.
15
in principle, the high value of Ocould be worked out ex ante on the basis of available
information, even if the calculations required to see this would be astronomically complex.
Now suppose that you have ﬁve thousand dollars to spend, and you want to use that
money to combat childhood blindness. We might take an awareness-restricted view of
your decision problem, on which you are deciding among donating to the half-dozen
most prominent international e orts to combat childhood blindness. In this problem,
swamping ASL may be relatively implausible. On the other hand, we might take an
awareness-unrestricted view of your decision problem, on which you are deciding among
any physically possible use of ﬁve thousand dollars to combat childhood blindness, in-
cluding options such as O. In this awareness-unrestricted decision problem, swamping
ASL may be more plausible. In this way, the prospects for swamping ASL may be sub-
stantially reduced once reasonable levels of option unawareness are incorporated into ex
ante decisionmaking.
So far, we have met three scope-limiting factors: rapid diminution, washing out,
and option unawareness. We saw that these scope-limiting factors are often present in
decisionmaking, and that, when present, they tend to diminish the prospects for swamping
ASL. But this does not imply that swamping ASL has empty scope. To see the point, let
us return to our discussion of the Space Guard Survey.
7 The good case revisited
In Section 3, I argued that swamping ASL may have accurately described a decision
problem facing Congress in the 1990s: whether to fund the Space Guard Survey, or to
redirect the money elsewhere. In support of that suggestion, note that all three of the
scope-limiting factors introduced above are largely absent from this example.
Begin with the problem of rapid diminution: the probabilities of large long-term
impacts diminish rapidly. The argument for rapid diminution drew on skepticism about
the persistence of short-term e ects into the long-term future. It is often hard to make
16
a persisting impact on the long-term future. But it is not hard to see how the proposed
eects of asteroid detection, namely preventing human extinction, could persist into the
long-term future.12Not being extinct is a status that can last for a very long time if we
play our cards right.
Turn next to the problem of washing out: possible long-term beneﬁts may be signiﬁ-
cantly cancelled by possible long-term harms. The ﬁrst argument for washing out drew
on evidential paucity: we don’t have much evidence about the long-term e ects of our
actions. But asteroid detection is an area in which we do have signiﬁcant evidence about
possible long-term e ects. This includes evidence from past asteroid impacts together
with a good scientiﬁc understanding of the determinants of asteroid impact force, which
is sucient to build compelling computational models of impact damages (Stokes et al.
2017).
Our second argument for washing out drew on forecasting skepticism: it is hard to
predict the future. First, I argued that in many areas we have no good track record of
predicting the far future. But astronomy is one of the few areas in which we have a
good track record of predictions on this time-scale. Second, I argued that experts are
often unwilling to make forecasts of the relevant type. But the key forecast driving the
example was a prediction by NASA scientists of the probability of catastrophic asteroid
impacts. Third, I argued that due to the multidimensionality of value we may only be able
to estimate the probability of a catastrophic impact, but not its value. But where human
extinction is concerned, this may not be a signiﬁcant problem. To evaluate whether
preventing human extinction would be a good thing, we must only answer a single
question: whether the continued existence of humanity would be a good thing. While
answering this question is not straightforward, many theorists are cautiously optimistic
that the future will be good (Beckstead 2013; Ord 2020; Parﬁt 2011).
Turn ﬁnally to the problem of option unawareness: decisionmakers are unaware of
12However, if we are pessimistic about current levels of existential risk, this point is no longer so clear
(Thorstad 2022).
17
some options which may be swamping longtermist options. But in the case of the Space
Guard Survey, we were already aware of feasible options which could produce the desired
results at a reasonable cost. It may well be true that other options, of which we were
unaware, would have been still better, but this does not mean that the options ultimately
chosen were not swamping longtermist options.
So far, we have seen that the scope-limiting factors do not threaten the case for swamp-
ing ASL in some cases, for example the decision to fund the Space Guard Survey. That
should be unsurprising: we did not expect the scope of swamping ASL to be completely
empty, and the Space Guard Survey is an example in which many decisionmakers agreed
with the longtermist’s evaluative claims. However, in many other examples the scope-
limiting factors begin to signiﬁcantly threaten the case for swamping ASL. The next section
provides an illustration.
8 Beyond the good case
Let us return to Beckstead’s case of a philanthropist deciding between various initiatives
for preventing childhood blindness. We have already seen that this case is subject to
signiﬁcant option unawareness, and that the presence of option unawareness tends to
reduce the plausibility of swamping ASL in this case. In the rest of this section, I suggest
that both of the remaining scope-limiting factors are also present in this case, and that
these factors further tell against the applicability of swamping ASL.
Begin with rapid diminution in the probabilities of large long-term impacts. The
argument for rapid diminution was that it is hard to make a persisting impact on the
long-term future. For example, Beckstead suggests that curing blindness may impact the
long-term future by helping treated individuals to contribute to their nation’s economic
development. But we saw in Section 4 that even large shocks, such as the detonation of
a thermonuclear bomb, are often insu cient to make lasting long-term impacts on the
economy of a medium-sized city, much less a nation. If that is right, then we should
18
substantially reduce our conﬁdence in the ability of any single individual to make a
persisting long-term economic impact. It is true, of course, that some individuals may
occupy prominent economic roles, for example the leadership of a large corporation. But
what is less clear is that, in the absence of these individuals, underlying demographic,
cultural and economic factors would have led the region down a substantially di erent
path.
Turn next to washing out: the tendency for long-term expected beneﬁts to be signiﬁ-
cantly cancelled by long-term expected harms. I think that we should expect signiﬁcant
washing out in this case. It is, of course, quite possible that the children we treat will go
on to ﬁght climate change or found a world government. But it is also possible that they
will go on to be among the world’s greatest polluters, or to oppose world government.
Nor, for that matter, can we be terribly certain which of these developments would be
for the long-term good. It might be that the premature move towards world government
would lead to tyranny, or to a governance failure that would set back the development
of more e ective systems by several centuries. And for that matter, we should not be
terribly conﬁdent that blindness will be an impediment to playing an important role in
any of these endeavors. Because we have very little evidence to go on in assessing the
likelihood of various far-future e ects that may result from treating childhood blindness,
we should tend to signiﬁcantly discount likely long-term beneﬁts by leaving open the real
possibility that our actions will produce long-term harms.
The discussion of childhood blindness helps us to see how quickly the scope-limiting
factors get a take on decisionmaking, even in cases that are often taken to motivate
swamping ASL. When the scope-limiting factors are present, the case for swamping ASL
becomes much more tenuous.
19
9 Conclusion
This paper assessed the fate of ex ante swamping ASL: the claim that the ex ante best thing
we can do is often a swamping longtermist option. I argued that swamping ASL may
hold in some cases, such as the decision to fund the Space Guard Survey. However, I
also discussed three scope-limiting factors which, when present in a decision problem, tend
to reduce the prospects for swamping ASL. These scope-limiting factors included rapid
diminution in the probabilities of large far-future beneﬁts; washing out between possible
positive and negative future e ects; and unawareness of swamping longtermist options.
I argued that swamping ASL may still be true in some cases, particularly when the
scope-limiting factors are not present. However, I suggested that the scope of swamping
ASL may be far narrower than often supposed. I used a discussion of treating childhood
blindness to illustrate how the scope-limiting factors get a take even on many cases taken
to motivate swamping ASL. I suggested that as the scope-limiting factors make themselves
increasingly felt, the prospects for swamping ASL diminish.
In some ways, this may be familiar and comforting news. For example, Hilary Greaves
(2016) considers the cluelessness problem that we are often signiﬁcantly clueless about
theex ante values of our actions because we are clueless about their long-term e ects.
Greaves suggests that although cluelessness may correctly describe some complex de-
cisionmaking problems, we should not exaggerate the extent of mundane cluelessness in
everyday decisionmaking. A natural way of explaining this result would be to argue that
in most everyday decisionmaking, it is the expected long-term e ects of our actions that
are swamped by their short-term e ects, and not the other way around. This would mean
that cluelessness about long-term e ects is often compatible with substantial conﬁdence
and precision in our views about the overall values of options.
In addition, this discussion leaves room for swamping ASL to be true and important
in some contemporary decision problems. It also does not directly pronounce on the fate
of ex-post versions of ASL, or on the fate of non-swamping ASL. However, it does suggest
20
that swamping versions of ASL may have a more limited scope than otherwise supposed.
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