http://www.faculty.ucr.edu/~eschwitz/SchwitzPapers/XWorld-121227.htm
Be Well.
David
Experimental Evidence for
the Existence of an External World
Eric Schwitzgebel
Department of Philosophy
University of California at Riverside
Riverside, CA 92521-0201
eschwitz at domain: ucr.edu
Alan T. Moore
Department of Philosophy
University of California at Riverside
Riverside, CA 92521-0201
December 27, 2012
Experimental Evidence for the Existence of an External World
Abstract:
In
this essay I attempt to refute radical solipsism by means of a series
of empirical experiments. In the first experiment, I prove to be a poor
judge of four-digit prime numbers, in contrast to a seeming Excel
program. In the second
experiment, I prove to have an imperfect memory for arbitrary-seeming
three-digit number and letter combinations, in contrast to my seeming
collaborator with seemingly hidden notes. In the third experiment, I
seem to suffer repeated defeats at chess. In all three experiments, the
most straightforward interpretation of the experiential evidence is
that something exists in the universe that is superior in the relevant
respects – theoretical reasoning (about primes), memorial retention (for
digits and letters), or practical reasoning (at chess) – to my
own solipsistically-conceived self.
Experimental Evidence for the Existence of an External World
It
occurs to me to wonder whether the external world exists – that is,
whether anything exists other than my own stream of conscious
experience. Radical solipsism, I’ll say, is the view that my
conscious mind is the only thing in
the universe; there are no material objects, no other minds, not even a
hidden unconscious side of myself. On radical solipsism, this [here
I gesture inwardly at my sensory, emotional, and cognitive experiences]
is all there is, nothing more. I find myself, now, contemplating
radical solipsism. I want some sort of evidence or proof of its
falsity.
You might think – if you exist – that my desire for proof is foolish. You might think it plain that I could never show radical solipsism to be false, that I (and you and we) can only assume that
it’s false, that any attempt to prove solipsism wrong would inevitably
turn in a circle. You might think, with (my seeming memory of)
Wittgenstein
(1950-1951/1974), that the existence of an external world is an
unchallengeable framework assumption necessary for any inquiry to make
sense, that it’s a kind of philosophical disease to want to rationally
refute solipsism, that I might as well hope to establish the validity of
logic using no logical assumptions or to hoist myself skyward by
tugging on my belt. Now I’ll grant that I might be philosophically
sick. There’s something admittedly crazy about solipsistic doubt. But
it’s not entirely clear to me, at least not yet, that I can’t find my
cure from within the disease, by giving my sick mind exactly the proof
it wants.
At first blush, the historical evidence – or what I think of as the historical evidence – looks unpromising. The two most
famous attempts to cure solipsism from within come from Descartes, in his Meditations(1641/1984), and Kant, in his “Refutation of Idealism” (from his first Critique: 1781/1787/1929). Both are conspicuous failures. Descartes’s proof
of the external world requires accepting, as an intermediate step, the
very dubious claim that the thought of a perfect God could only arise
from a being as perfect as God.[1] Kant’s
proof turns on the assertion that I cannot be “conscious of my own
existence as determined in time” or conscious of change in my
representations unless I perceive some permanent things that actually
exist outside of me. This is also a very dubious claim, and one for
which he offers no clear argument. Why couldn’t a sense of
representational change and of my determination in time arise innately
or from temporally overlapping experiences or from hallucinatory
experiences as of seeing things that exist outside of me?[2] Most
philosophers today, I think, regard as hopeless all such attempts to
prove radical solipsism false using as one’s starting point only general
logic and solipsism-compatible premises about one’s own conscious
experience.
So
we might, with Hume (1740/1978), yield to the skeptic and grant her the
argument, then turn our minds aside for a while, play some backgammon,
and go on living and philosophizing (on other topics) just as
before. Or we might, with Moore (1939), refute the solipsist by proving
that the external world exists by means of solipsism-incompatible premises
that beg the question. “Here is a hand, here is another, therefore the
external world exists; what, you want stronger proof than that?”
is really just a refusal to play the intended game. Or we might, with
Wittgenstein, try to undercut the very desire for proof. However, none
of these responses seems to me to be preferable to actually delivering a
non-question-begging
proof if one is discoverable. They are all fallback maneuvers. Another type of fallback maneuver, I think, can be found in those recent versions of contextualism and reliabilism that
concede to the radical solipsist that we cannot know that the external
world exists, once the question of its existence has been raised in a
philosophical context, while insisting that we can still nonetheless
have ordinary knowledge of the mundane facts of practical life.[3]
The
historical landscape has been dominated by these two broad
approaches. The first approach aims high, hoping to establish with
apodictic or deductive or “transcendental” certainty, in a
non-question-beggingway, that the external
world really does exist. The second approach abandons hope of
non-question-begging proofs, seeking in one way or another to make us
comfortable with their absence. But there is a third approach,
historically less influential, that has not yet, I think, been
adequately explored. Its most famous advocate is Bertrand Russell.
Russell writes:
In one sense it must be admitted that we can never prove the
existence of things other than ourselves and our experiences.... There
is no logical impossibility in the supposition that the whole of life
is a dream, in which we ourselves create all the objects that come
before us. But although this is not logically impossible, there is no
reason whatsoever to suppose that it is true; and it is, in fact, a less
simple hypothesis, viewed as a means of accounting for the facts of our
own life, than the common-sense hypothesis that there really are
objects independent of us, whose action on us causes our sensations
(1912, p. 22-23, emphasis in original).
Russell
also states that certain experiences are “utterly inexplicable” from
the solipsistic
point of view and that the belief in objects independent of us “tends
to simplify and systematize our account of our experiences”, and for
this reason the evidence of our experience speaks against solipsism, at
least as a “working hypothesis” (1912, p. 23-24; 1914, p.
103-104). Russell aims lower than do Descartes and Kant; and partly as a
result his goal seems more plausibly attainable. Yet Russell also
promises something that the Hume, Wittgenstein, Moore, et al. do not: a
non-question-begging positive argument against solipsism. It’s a kind
of middle path between certainty and surrender or refusal.
Unfortunately,
there are two major shortcomings in Russell’s argument. One is
Russell’s emphasis on simplicity. The most natural way to
develop the external world hypothesis, it seems, involves committing to
the real existence of billions of people, many more billions of
artifacts, and naturally-occurring entities vastly more numerous even
than that, manifesting in highly complex and unpredictable patterns. On
the face of it, it’s odd to say that such a picture of the world is
simpler than radical solipsism.
The second shortcoming is the uncompelling, gestural nature of Russell’s supporting examples. What is it, exactly, that Russell says is “utterly inexplicable” for the solipsist? It is a cat’s seeming hunger, after an interval during which the cat was not experienced:
if [the
cat] does not exist when I am not seeing it, it seems odd that appetite
should grow during non-existence as fast as during existence. And if
the cat consists only of sense-data, it cannot be hungry,since no hunger but my own can be a sense-datum to me. Thus the behaviour of
the sense-data which represent the cat to me, though it seems quite
natural when regarded as an expression of hunger, becomes utterly
inexplicable when regarded as mere movements and changes of patches of colour, which are as incapable of hunger as a triangle is of playing football (p. 23, emphasis in original).
To
this example, Russell appends a second one: that when people seem to
speak “it is very difficult to suppose that what we hear is not the
expression of a thought” (p. 24). But are such experiences really so utterly
inexplicable for the solipsist? I can begin to frame some possible
solipsism-compatible explanations. Maybe I can start by thinking about
what seems to happen in dreams. Indeed, Russell’s very next sentence
expresses the obvious objection from dreams. Dreams arguably can
involve apparent hungry cats and apparent human voices.[4] Appearances
of hungry feline behavior, then,
if they can happen explicably in dreams, needn’t require real feline
hunger behind them to be explicable, contra what Russell seems to be
assuming in his argument; nor need appearances
of human speech require real human minds independent of my
own. Although this objection seems to me to be entirely fatal to
Russell’s argument as stated, Russell appears to be satisfied to give
only a cursory, single-sentence response: “But dreams are more or less
suggested by what we call waking life and are capable of being more or
less accounted for on scientific principles if we assume that there
really is a physical world” (p. 24). The inadequacy of this response is
revealed by the fact that the solipsist can say something quite
similar: If I assume solipsism then I can account for the
appearances of the cat and the interlocutor as imperfect projections of
myself upon my imagined
world, grounded in what I know about myself though introspection. Such
an explanation is sketchy, to be sure, but so also – notoriously – is
the current scientific explanation of dreams. At best, Russell’s
argument is problematically underdeveloped.
Although
I am dissatisfied with (what I think of as) Russell’s particular
argument, as I sit here (or seem to) with my solipsistic doubts, I still
feel the attraction of that general approach. The core idea I want to
preserve is this: Although in principle (contra Descartes and
Kant) all the patterns in my experience are compatible with the
non-existence of anything behind that experience, I still can entertain
two competing hypotheses about the origins of those experiences: the
solipsistic hypothesis
according to which all there is in the universe are those experiences
themselves, and the external world hypothesis which holds that there is
something more. I can then consider these hypotheses not by the
standards of apodictic or transcendental proof, but rather as something
like scientific hypotheses, with epistemic favor accruing to the one
that appears to do the better job accounting for the experiential
evidence at hand. Although Russell’s own remarks are too cursory, that
doesn’t speak against the general project. Indeed, it invites the hope
that a more patient effort might still bear fruit.[5]
I
hope to take Russell’s approach one step farther. Russell treats the
solipsistic hypothesis and the external world hypothesis as scientific
or quasi-scientific hypotheses that have different theoretical virtues
and vices when confronted with the task of explaining his apparent
sensory experiences. But neither he nor later philosophers sympathetic
with this general approach – see Beebe (2009) for a review – actually empirically test the
two competing hypotheses, to see which hypothesis makes more accurate
predictions given plausible solipsism-compatible auxiliary
assumptions. No one in the tradition – or rather, I should say, no
apparent person in what I think of as the tradition – sets up an actual
series of experiments, in formal scientific style, pitting the two
hypotheses against each other in a non-question-begging way and then
quantitatively analyzing the results. No one transforms Russell’s
vaguely scientific appeal into actual experimental philosophy. That is what I aim to do in this essay.
In
other words, I aim to do some solipsistic science. There is no
contradiction in this, I think. Skepticism about the external world is
one thing, skepticism about induction and scientific reasoning quite
another. I aim to see whether, from assumptions and procedures that
even a radical solipsist can admit, I can generate experimental evidence
for the existence of an external world.
Let
me emphasize: I don’t hope to prove something from nothing. The
skeptic’s position is unassailable if his opponent must prove all the
premises of any potential argument. All scientific procedures must rest
on some background assumptions that are taken for granted. I aim to
refute not all of skepticism, but rather only radical solipsism. I aim only
to move from solipsism-compatible premises to an anti-solipsistic
conclusion. That, I think, would be interesting enough and victory
enough. Consequently, for purposes of this project, I don’t plan to
entertain any more than the usual doubt about (solipsism-compatible
versions of) induction or deduction or memory or introspective
self-knowledge.
More specifically, I will allow myself to assume the following:
· introspective knowledge of sensory experience and of other happenings in the stream of experience;
· memories of past experience from
the time of the beginning of the series of experiments (but not before);
· concepts
and categories arrived at I-know-not-how and shorn of any
presupposition of grounding in a really-existing external world;
· the general
tools of reason and scientific evaluation to the extent those rules
don’t build in any assumptions about affairs beyond my stream of
experience.
Leaning
only on these resources, I will try to establish, to a reasonable
standard of scientific confidence, the existence of an external world.
If
solipsism implies that I have complete control over my stream of
experience, it would be easy to refute experimentally. I might, for
example, take in my hands a deck of cards (or at least seem to myself to
do so) and resolutely will that I draw a queen of clubs. Then I
might note the failure of the world to
comply with my will. In fact, I have now attempted exactly this, with
an apparent ten of diamonds as my result. But unfortunately for the
prospects of such an easy proof, solipsism has no such voluntaristic implications and thus admits of no such anti-voluntaristic refutation.[6]
To
think through this last issue more clearly, I close my eyes – or rather
I do something that seems to me to be a closing of the
eyes. What I visually experience is an unpredictable and
uncontrollable array of colors against a dark gray background, the Eigenlicht.[7] This uncompliant Eigenlicht is entirely compatible with radical solipsism as long as I conceptualize the patterns it contains as nothing but patterns in, or randomnesses in,my
stream of sensory experience, patterns governed by their own internal
coherences rather than by anything further that stands behind
them. The unpredictability and uncontrollability of these visual
patterns no more compels me to accept the existence of non-experiential
objects than irresolvable randomness and unexplained laws in the
material world, as I conceptualize it, would compel me to accept the
existence of immaterial objects behind the material ones.
What
sorts of tests, then, might put radical solipsism at
risk? Interpreting this question as straightforwardly as possible, I
see three types of potential evidence that would be difficult to
accommodate on a solipsistic view: evidence of the existence of
something with theoretical reasoning powers that exceed my own, evidence
of the existence of something that can retain its properties over a
period during which those properties are lost to my
sensory experience and memory, and evidence of something with practical
reasoning powers that exceed my own.
I
will now describe three experiments, all conducted in one uninterrupted
episode on a single day. To the extent possible, the remaining text,
apart from the final concluding section, reflects real thoughts on the
day of experimentation, with a few subsequent modifications for
clarity. To fit all of these thoughts into the time-span of a single
day, I drafted a version of the material below in the present tense
using dummy results based on pilot experiments. I entered into the
experiment with the intention of genuinely thinking the thoughts below
with real data as the final results came in. Where the results
surprised me, I of course had to
modify my thinking.
Experiment 1: The Prime Number Experiment.
Method. I
have prepared for this experiment by doing something that seems to me
to be an instance of programming Microsoft Excel to calculate whether a
four-digit number is prime, displaying “prime” next to the number if it
is prime and “nonprime” if it is not. Then I did something that seemed
to me to be programming Microsoft Excel to generate arbitrary numbers
between 1000 and 4000, excluding numbers divisible by 2, 3, and
5. Version A of this experiment will proceed in
four stages, if all goes according to plan. First, I will generate a
fresh set of 20 new qualifying four-digit numbers. Second, I will take
my best guess at which of those 20 numbers are prime, allotting myself
approximately two seconds for each guess. Third, I will paste this set
of numbers into my seeming prime number calculator function, noting
which ones are marked as prime by the seeming machine. Finally, by
laborious hand calculation, I will determine which among those twenty
numbers actually are prime. Version B will proceed the same way, except using Roman numerals as the initial basis for my guesses.
My
hypothesis is this: If nothing exists in the world apart from my stream
of conscious experience,
then the swift, seemingly Excel-generated answers should not be
statistically more accurate than my own best guesses. For if they were
more accurate, that would suggest that something exists in the world
that has calculation powers that exceed my own.
Results. I
have just now conducted the experiment as described. Then main results
are displayed in Figure 1. For Version A, my best guesses yielded an
estimate of 11 primes. In most cases, this felt like simplehunchy guessing,
though 3913 did pop out as nonprime. The apparent Excel calculation
also yielded an output of 11 seemingly machine-calculated
primes. Subsequent hand calculation confirmed the
seeming machine results in 19 out of the 20 cases. (I leave it open
for purposes of the experiment whether the failure of match in one case
reflects computational error on my part.[8]) In
contrast, hand calculation confirmed my best-guess judgments in only 11
out of the 20 cases. The difference in accuracy between 19/20 and
11/20 is statistically significant by Fisher’s exact test (hand
calculated), with a two-tailed p value of < .02. For Version B,
again both my best guesses and the apparent Excel outputs yielded 11
estimated primes, and again hand calculation confirmed the apparent
Excel outputs in 19 of the 20
cases,[9] while
hand calculation confirmed my best guesses in 13 of the 20 cases. The
difference in accuracy between 19/30 and 13/20 is marginally significant
by Fisher’s exact test (hand calculated), with a two-tailed p value of
approximately .05.[10]
Figure
1: Accuracy of prime number estimates, as judged by hand calculation,
for my best guesses before calculating, compared to what would seem to
be the output of an Excel spreadsheet programmed to detect primes. Error
bars are hand-calculated 95% confidence intervals using the normal
approximation and a ceiling of 100%.
Discussion. I believe the most natural interpretation of these results is that something exists in the external
world that has calculation capacities exceeding my own.
I set aside radically skeptical concerns about memory (what if the world was created two seconds ago?) and introspection[11] (what if I delusionally misjudged
all my intentions and/or sensory experiences?). My aim, as I have
emphasized, is not to employ radically skeptical standards generally,
but rather to employ (what I think of as) the normal standards of
science insofar as they can be employed by
someone open-minded about radical solipsism. I also set aside concerns
about whether this seeming computer really calculates rather than only being designed to give outputs interpretable by users as the results of calculation.[12] Either
way, the results suggest the existence of someone or something with
prime-number-detection capacities that exceed those present in my solipsistically-conceived
stream of experience. That thing might even be my own unconscious
mind, bent on tricking my conscious mind into misinterpreting my
experimental results. No
problem! Radical solipsism as I’ve defined it would still be false,
since radical solipsism denies the existence of anything outside of my stream of experience, even if only my own unconscious mind.
As
I reflected earlier, I believe that solipsism can readily allow that
the stream of experience contains patterns within it, as long as those
patterns are not caused by anything behind that experience. The
anti-solipsistic interpretation of these results thus turns crucially on
the question of whether the outcome of this experiment might plausibly
be only a manifestation of such solipsistic patterns of experience. So:
How plausible would such a pattern be, really, given solipsistic
assumptions? What should I
expect patterns of experience to look like if solipsism is true?
These are hard questions to answer. And yet I don’t want to be too hard on myself. I’m looking only for scientific plausibility, not absolute certainty.
One
typical kind of pattern in experience, it seems to me, is this: When I
do something that feels like shifting my eyes to the left, my
experienced visual field seems to shift to the right – a fairly simple
law of experience, a simple way in which two experiences might be
directly related with no compelling explanatory need of a
non-experiential intermediary. Likewise, when I seem to
see a spherical thing and then seem to reach out to touch it, I seem
also to have tactile experience of something spherical. This pattern is
somewhat more complex, and not fully expressible by me, but still it
seems a fairly straightforward set of relationships among
experiences. It’s tempting to think that there must be a genuine
mind-independent physical sphere that unifies and structures those
cross-modal experiences. But if I am to be genuinely open-minded about
solipsism, I think I must admit that the existence of a radically new
ontological type is a heavy cost to pay to explain this set of
experiences. They might be related to each other directly by an
admittedly somewhat complex set of intrinsically experiential laws (as
in Mill 1867). Similarly when I close my eyes. There
are regularities – the visual field changes radically in roughly the
way I
expect, though it also gains some highly unpredictable
elements. Solipsism can also allow, I think, the existence of
unrecognized patterns of relationship among my experiences. For
example, afterimages of bright seeming-objects might be in perfect
complementary colors even if I don’t realize that fact. There might be
discernible but as-yet-undiscerned regularities
governing temporal evolutions in the flight of colors I experience when
my eyes are closed. All of this seems plausibly explicable by
solipsistic laws that relate experiences directly, one to another. And
all of this I was ready to admit before I began my experiment. I am
simply reminding myself. I intended that my experiment tap into
something different.
To explain the results of Experiment 1 solipsistically via
such unmediated laws of experience, something like the following would
have to be true. There would have to be an unmediated relationship
between, on the one hand, (a.) the visual experience, for example, of
the numeral “2837” in apparent black Calibri 11 font in an apparent
Excel spreadsheet, accompanied by the inner speech experience of saying
to myself, with understanding, “twenty-eight thirty-seven” in English,
and, on the other hand (b.) the visual experience of suddenly seeing
“prime” in the matched column to its right if the number is prime or
“nonprime” if the number is nonprime. Such a law would be both semantic
and dependent upon facts about primes in a way that I tend to think of
as uncharacteristic of scientific laws. In both ways it’s quite
different from the laws of
experience I described in the previous paragraph. Furthermore, such
laws would have to work in essentially the same way for Roman numerals
too, despite the fact that Roman and Arabic numerals have little in
common on the sensory surface. Something in the world seems to be
responding, more swiftly than I possibly can, to semantic facts about
the primeness of the numbers represented
by these different numerals, producing the complex visual shapes “prime”
and “nonprime” appropriately in response.
Now maybe this is indeed just a previously unknown type of law of experience. Maybe the primeness of
the number represented by the arbitrary visual shape of a numeral can
indeed have direct effects
on later visual experiences of mine without need of anything beyond my
stream of experience. But it seems to me rather a strain to think
so. It doesn’t seem the most natural prediction from a solipsistic
point of view. Positing such a law in response to the evidence of
Experiment 1 has the scent, I think, of a suspiciously ad hoc maneuver
designed to save a theory from what would otherwise be counterevidence –
the classic sign of a theory in trouble, per Duhem (1906/1954), Popper (1934/1959), Kuhn (1962/1996), Lakatos (1978)
– whereas it is just what I would predict if the external world exists
and has the sorts of features (like functional spreadsheet programs)
that I would like to believe it has.
Given
my acknowledged bias against solipsism, though, it would be imprudent
to leap too swiftly to the conclusion that solipsism is false from this
evidence alone. Maybe this is exactly the sort of law of experience
that I should expect on a solipsistic worldview, charitably enough
understood. So I have some further experiments in mind.
Experiment 2: Two Memory Tests.
Method. If
the external world exists, it might contain a person named Alan, whom I
am inclined to think of as my graduate student collaborator. I have
arranged with this seeming “Alan” that he test my memory. In the first
test, he will orally present to me an arbitrary-seeming series of 20
three-digit numbers. He will present this list to me twice. I will
first attempt to freely recall items from that list, and then I will
attempt to recognize those items from among a 40-item list, half of
which consists of new three-number combinations. The second test will
be the same procedure with 20 sets of three letters each, and with a
two-minute enforced delay to further impair my performance. In both
cases, I expect that seeming-Alan will tell me that my memory has been
less than perfect. He will then, if all goes according to plan, tell me
that he is visually re-presenting the original lists. If solipsism is
true, nothing should exist to anchor the advertised visual
“re-presentation” to the earlier orally-presented lists,
apart from my own memory. In those cases, then, where my memory has
failed, the supposed “re-presentation” should not contain a greater
number of the originally presented elements than would be generated by
chance. I shouldn’t be able to step in the same stream twice except
insofar as I can remember that stream (though maybe I could have the
illusory feeling of having done so). The contents of experience should
not have a fixity that exceeds that of my memory, because there is
nothing beyond my own experience that can do the fixing. At least, this
seems to me the most straightforward prediction from within the
solipsistic worldview.
The
final move in the experiment will be to confirm that the re-presented
list does indeed match the original list despite
the gap in my memory. The method of confirmation will be this:
Seeming-Alan will state the procedure by which he generated the
seemingly arbitrary lists. By (seeming) prior arrangement, he will have
used a simple semantic procedure for the letters and a simple
arithmetic procedure for the numbers. (I seem to recall having
suggested that he draw his letters from something like the middle three
letters of each U.S. state in alphabetical order or that he take a
string of text I would recognize and present it backwards, and that he
draw his numbers from something like the decimal expansion of 1/n for
some n that generates a suitably complicated expansion.) I should then
be able to confirm that the later-presented full lists of 20
three-element items are indeed consistent with generation by the claimed
procedures. This will in turn suggest that the original lists were
also generated by those same
procedures. It will do so, if all goes well, because (as I will later
estimate) there’s only a very small chance that two arbitrary lists of
20 three-element items would have several items in common – the several
items I hope to remember across the temporal gap – unless they were
generated by the same procedure. This would then allow me to infer that
the entire “re-presented” list does indeed match the entire original
list despite my failure to recall some items across the interval –
contra the no-same-stream prediction of the solipsistic hypothesis.
Results. The
main results are displayed in Figure 2. According to seeming-Alan, in
the number test, I correctly recalled 7 of the 20 three-digit items
(with no false
recall) and I accurately recognized 14 of the items. In the letter
test, I correctly recalled 8 of the 20 three-letter items (with no false
recall) and accurately recognized 18. The generating patterns, he
claims, were the decimal expansion of 1/2012, excluding the initial
zeroes, and the most famous lines of Martin Luther King, Jr.’s, “I Have a Dream” speech, skipping every other letter and excluding one repeated item. In both cases I hand-confirmed that the “re-presented” lists conformed to the purported generation procedure. Hand
application of the two-tailed Fisher’s exact test shows recall to match
significantly less well to the “re-presented” lists than do the
hand-confirmation results (both p’s < .001). At a p < .05 confidence level, the recognition results are statistically
significant for the three-digit items but not the three-letter items.
Figure 2: Number
correct out of 20 as judged by comparison with the lists “re-presented”
by seeming-Alan, for my recall guesses, my recognition-test guesses,
and my hand confirmation of the purported generating procedure. Error
bars for “recalled” and “recognized” are hand calculated 95% confidence
intervals using the normal approximation. Error bars for the
hand-confirmed data use the “rule of three”. See
the body of the text for statistical tests.
I
found myself trying hard in both memory tasks. Since I am inclined to
believe that the external world does exist and thus that some other
people might read what I now appear to be writing, I was motivated not
to come across as stupid. This created a substantial incentive to
answer correctly which I did not feel as strongly in Experiment 1.
Discussion. I
believe the most natural interpretation of these results is that
something existed in the external world that retained the originally
presented information across my gap of memory.
Alternative
interpretations are possible as always. The question is whether those
alternative interpretations are scientifically attractive. One
alternative interpretation is that the laws connecting experiences are
temporally gappy or even temporally
backwards. There might have been a direct, unmediated connection
between the experience of hearing the original auditory experience of
“IAE”, “DEM”, etc.,
and later visually experiencing those same letter arrangements. If I
am willing to countenance backward causation, then a neat explanation
offers itself: I might have solipsistically concocted
the generating patterns at the moment seeming-Alan seemed to be
informing me of them, and then these generating patterns might have
backwardly caused my initial auditory experiences and guesses. However,
temporally backward causation seems a desperate move if I’m aiming to
apply normal scientific standards as I conceptualize them. A somewhat
less radical possibility is temporally gappy cross-modal
causation from auditory experience at the beginning of the experiment
to visual “re-presentation” later; but this requires, in addition to the
somewhat uncomfortable provision of temporally gappy causation,
a further
seeming implausibility absent from the backward causation case – the
seeming implausibility, similar to that in Experiment 1, of an
unmediated law of experience that operates upon semantic contents of
those experiences that are unrecognized as such by me at the time of the
law’s operation. In this case the relevant semantic contents would be
nothing as elegant as primeness but
rather the decimal expansion of one divided by the current calendar
year, excluding the initial zeroes, and the English orthography of the
words of a famous speech, skipping alternate letters and excluding one
repeated triplet.
The thought occurs to me that some of the laws of external-world psychology, as I conceive of it, are also weird and semantical. For
example, an advertisement might trigger a tangentially associated
memory. But the crucial difference is this: In the case of
external-world psychology, the semantic associations, even if not
conscious, I assume to be grounded in mundane facts about neural firing
patterns and the like. A bare solipsistic tendency to create and then
recreate, unbeknownst to myself, the same partial orthography of a
famous speech, while meanwhile being unable to produce that partial
orthography when I consciously try to do so – well, that’s not
impossible perhaps, but neither does it seem as natural a development of
solipsism as does the view that the stability of experience should not
exceed the stability of memory.
My
argument would be
defeated if I could have easily found some simple scheme, post-hoc,
that could generate twenty items including exactly those seven recalled
numbers and eight recalled letter sets. My anti-solipsistic
interpretation requires that there be only one plausible generating
scheme for each set; otherwise there is no reason to think the
unrecalled items would be the same on the initially presented list as on
the subsequently presented list. So, then, what are the odds of a
post-hoc fit of seven or more items from each set? Fortunately, very
low – about one in a million, given some plausible assumptions and the
mathematics of combination.[13]
Perhaps,
then, the best defense for solipsism, if it’s not to collapse into a
general radical skepticism about memory or induction or arithmetic, is
temporally gappy forward causation
grounded in unrecognized weird semantic features of the relevant
experiences. I’m inclined to think this is a somewhat awkward position
for the solipsistic hypothesis. But maybe I’m being too unsympathetic
to solipsism? Maybe I should have expected that scientific laws would
look somewhat weird in a solipsistic world, and rather unlike the
scientific laws I think of as characteristic of the natural sciences and
naturalistic psychology? So I have planned for myself one final
experiment of a
rather different sort.
Experiment 3: Defeat at Chess.
Method. Seeming-Alan
has, if I recall, told me that he is good at chess. I believe that I
stink at chess. Thus, I have arranged to play 20 games of speed chess
against seeming-Alan, with a limit of approximately five seconds per
move. If solipsism is true, nothing in the universe should exist that
has chess-playing practical reasoning capacities that exceed my own, and
so seeming-Alan should be unable to defeat me at rates above
statistical chance. Figure 3 displays the procedure,
as presented to me by a seeming camera held by a seeming Gerardo
Sanchez.
Figure 3: The procedure of Experiment 3.
Results. Seeming-Alan
defeated me in 17 games of 20, with one stalemate. 17/19 is
statistically higher than 50% with a p-value < .001 (hand
calculated).
Discussion. It
occurs to me that I might have hoped to lose, so as to generate results
confirming my
preferred hypothesis that the external world exists. Against this
concern, I reassure myself with the following thoughts. If it was an unconscious desire
to lose, then that implies that something exists in the world besides
my stream of conscious experience, namely, an unconscious part of my
mind, and thus radical solipsism as I have defined it is false. If it
was, instead, a conscious desire to lose, I should have been able
to detect it, barring an unusual degree of introspective
skepticism. What I detected instead was a desire to win as many games
as I could manage, given my background assumption that if Alan actually
exists I would be hard pressed to win even one or two games. I found
myself forcefully and repeatedly struck by the impression that the
universe contained a practical intelligence superior to my own and bent
on defeating me. The most
natural scientific explanation of the pattern in my experience is that
that impression was correct.
Does
it matter that, if the external world exists in something like the form
I think it does, some chess-playing programs could have defeated me as
handily as seeming-Alan did? I don’t see why it should. Whether the
strategy and intentionality is manifested directly by a human being or
instead through the medium of a human-programmed chess-playing computer –
or in any other way – as long as that strategy and intentionality
exceeds the abilities of my own conscious mind, the solipsistic
hypothesis faces a substantial explanatory challenge. It can try to
address this challenge by appealing to intrinsic relationships among
experiences of mind –
relationships among seeming chess moves countered by other seeming
chess moves whose power I only recognize in retrospect – but the more
elegant unifying explanation of the results would seem to be the
existence of a hostile goal-directed intelligence.
I might easily enough dream of
being consistently defeated in chess. But dreams of this sort, as I
seem to remember, differ from the present experiment in one crucial way:
They are vague on the specific moves or unrealistic about those
moves. In the same way, I might dream of proving Fermat’s last
theorem. Such cases involve dream-like gappiness or irrationality or delusive credulity – the type of gappiness or
irrationality or delusive credulity that might make me see nothing
remarkable in discovering I am my own father or in discovering a new
whole number between 5 and 6. Genuine dream doubt might involve doubt
about my basic rational capacities, but if so, such doubts outrun simply
solipsistic doubts. And whether I am dreaming or not, if I
consistently experience clever and perceptive chess moves that
repeatedly exploit flaws in my own conscious strategizing, flaws that I
experience as surprising, it seems hard to avoid the conclusion that
something exists that exceeds my own conscious intelligence in at least
this one area.
General Discussion.
When
I examine my stream of experience casually, nothing in it seems to
compel the rejection of solipsism. My experience contains seeming
representations of outward objects; it follows patterns unknown to me
and that resist my will. But those basic facts of experience are
readily compatible with the truth of radical solipsism. Once I find
myself with solipsistic doubts, “here is a hand” does not help me
recover; but neither do ambitious proofs in the spirit of Descartes and
Kant seem to succeed. I could try to reconcile myself to the
impossibility of proof, but that feels like giving up.
Fortunately,
the external world hypothesis and the solipsistic hypothesis do appear
to make
different empirical predictions under certain conditions, at least when
interpreted straightforwardly. The external world hypothesis predicts
that I will see evidence of theoretical reasoning capacities, memorial
retention, and practical reasoning capacities exceeding my own, while
solipsism predicts the contrary. I can then scientifically test these
predictions, avoiding begging the question by using only tools that are
available to me from within a solipsistic perspective.
The
results come out badly for solipsism. To escape my seemingly
anti-solipsistic results requires either adopting other forms of radical
skepticism in addition to solipsism (for example about memory, even in
the short duration of these studies) or adopting increasingly ad hoc,
strained, and
convoluted accounts of the nature of the laws connecting one experience
to the next.
Did
I really need to do science to arrive at this conclusion,
though? Maybe instead of running formal experiments could I have simply
consulted long-term memory for evidence of my frustration by superior
intelligences and the like? Surely so! And thus maybe also even before
conducting these exercises I implicitly relied upon such evidence
informally to support my knowledge that the external world
exists. Indeed, it would be nice to grant this point, since then I can
rightly say that I have known for a long time that the external world
exists. But still, the present procedure, if successful, has several
advantages over attempts to remember past frustrations and
failures. For one thing, it achieves its goal despite conceding more
to the skeptic from the outset, for example about long-term memory. For
another, it more rigorously excludes chance and confirmation bias in
evidence selection. And for still another, it
forces me starkly and explicitly to consider the evidence and possible
alternative explanations of it in light of specific and concrete pieces
of data.
Perhaps
it’s worth noting that the best experiments I could concoct all
involved pitting my intelligence against another intelligence, or
against a device created by another intelligence – a device or
intelligence capable of generating semantic or strategic patterns that I
could only subsequently appreciate. Whether this is an
accidental feature of the experiments I happened to devise or whether
it reflects some deeper truth, I am unsure.[14]
I
conclude that the external world does in fact exist. To be clear, I
don’t at this point conclude anything about its metaphysical
character. It is consistent with my experimental results that the
external world bematerial or divine or an unconscious part of myself or an ectoplasmic computer, as long
as it can host intelligence. I’ll go out on a limb, though, and tentatively conclude that Alan exists[15] so
that I may call him co-author, and I will do something that seems to me
to be the act of circulating this essay for him and others to read.[16]
References
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Macmillan.
BonJour, Laurence (2002). Epistemology. Lanham: Rowman & Littlefield.
Broughton, Janet (2002). Descartes’s method of
doubt. Princeton: Princeton.
DeRose, Keith (1995). Solving the skeptical problem. Philosophical Review, 104, 1-52.
Descartes, René (1641/1984). Meditations on first philosophy. In J. Cottingham, R. Stoothoff, and D. Murdoch, eds., The philosophical writings of Descartes, vol. II. Cambridge: Cambridge.
Dicker, Georges (2008). Kant’s refutation of idealism. Noûs, 42, 80-108.
Dretske, Fred (2003). Skepticism: What perception teaches. In S. Luper, ed., The skeptics. Aldershot, England: Ashgate.
Duhem, Pierre (1906/1954). The aim and structure of physical theory. Trans. P.P. Wiener. Princeton: Princeton.
Fichte, Johann G. (1797/2000). Foundations of natural right. Ed. F. Neuhouser. Trans. M. Bauer. Cambridge: Cambridge.
Guyer, Paul (1987). Kant and the claims of knowledge. Cambridge: Cambridge.
Hegel, G.W.F. (1807/1977). Phenomenology of spirit. Trans. A.V. Miller. Oxford: Oxford.
Hume, David (1740/1978). A treatise of human nature, ed. L.A. Selby-Bigge and P.H. Nidditch. Oxford: Oxford.
Kant, Immanuel (1781/1787/1929). Critique of pure reason. Trans. N.K. Smith. New York: St Martin’s.
Kuhn, Thomas S. (1962/1996). The Structure of Scientific Revolutions, 3rd Edition. Chicago: Chicago.
Lakatos, Imre (1978). Philosophical papers, ed. J. Worrall and G. Currie. Cambridge: Cambridge.
Lewis, David (1996). Elusive knowledge. Australasian Journal of Philosophy, 74, 549-567.
Mill, John Stuart (1867). An
examination of Sir William Hamilton’s philosophy. London: Longmans, Green, Reader, and Dyer.
Moore, G.E. (1939). Proof of an external world. Proceedings of the British Academy, 25, 273-300.
Nolan, Lawrence, and Alan Nelson (2006). Proofs for
the Existence of God. In Stephen Gaukroger, ed., The Blackwell Guide to Descartes’ Meditations. Oxford: Blackwell.
Popper, Karl R. (1934/1959). The logic of scientific discovery. New York: Basic.
Russell, Bertrand (1912). The problems of philosophy. Oxford: Oxford.
Russell, Bertrand (1914). Our knowledge of the external world. London: George Allen & Unwin.
Schwitzgebel, Eric (2011). Perplexities of consciousness. Cambridge, MA: MIT.
Schwitzgebel, Eric (2012). Introspection, what? In D. Smithies and D. Stoljar, eds., Introspection and consciousness. Oxford: Oxford.
Searle, John R. (1980). Minds, brains, and programs. Behavioral and Brain Sciences, 3, 417-457.
Searle, John R. (1984). Minds, brains and science. Cambridge, MA: Harvard.
Stern, Robert (2012). Is Hegel’s master-slave
dialectic a refutation of solipsism? British Journal for the History of Philosophy, 20, 333-361.
Stroud, Barry (1984). The significance of philosophical scepticism. Oxford: Oxford.
Stroud, Barry
(1994). Kantian arguments, conceptual capacities and invulnerability. In P. Parrini, ed., Kant and contemporary epistemology. Dordrecht: Kluwer.
Vogel, Jonathan (1990). Cartesian skepticism and inference to the best explanation. Journal of Philosophy, 87, 658-666.
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[1] See discussion in Broughton 2002; Nolan and Nelson 2006. Broughton explicitly notes that few readers of the Meditations have found this aspect of Descartes’s argument plausible (2002, p. 154).
[2] Even
sympathetic commentators seem to agree that Kant’s argument is
problematic. For charitably amended reconstructions in light of
subsequent Kantian texts – excessively charitable, I’m inclined to
think, and still unsuccessful as proofs – see Guyer 1987
and Dicker 2008. See also Stroud 1984 and 1994 for a more general
critique of Kantian “transcendental” refutations of skepticism.
[3] See, e.g., Williams 1991; DeRose 1995; Lewis 1996; Dretske 2003.
[4] I
have to admit, however, some attraction to the view that dreams
typically involve not perceptual experiences but rather imagery
experiences (Ichikawa
2009). I don’t think that affects my general complaint against
Russell’s argument, however. If necessary, the arguments of this
paragraph could be reframed using hallucination, or the solipsist
explanation could even be sui generis without an obvious parallel in
commonsense views about the ordinary causes of non-veridical experience.
[5] Some other recent epistemologists have also expressed hope for such a project – notably Jonathan Vogel (1990),
Laurence BonJour (2002), and James Beebe (2009) – though their efforts, like Russell’s, remain largely gestural and promissory.
[6] Certain
remarks of Berkeley (1710/1965, §29 ff.) and Fichte (1797/2000, §2)
suggest a view of solipsism on which the solipsist has full voluntary
control of all experience. But such compliant-world solipsismis a flimsy cousin of the more robust version of solipsism I have in
view. See also Descartes 1641/1984, Meditations 3 and 6.
[7] For more on visual experience with one’s eyes closed, including the question of controllability, see Schwitzgebel 2011, ch. 8.
[8] Subsequent
examination of my notes suggests a long-division error on my part and
thus that the apparent Excel output was correct after all.
[9] Subsequent
examination of my notes reveals an error in my hand conversion from Roman to Arabic numerals.
[10] I
did not attempt precise hand calculation of the p value for this
test. Subsequent analysis with a statistical program yields p =
.044. For Version A, subsequent analysis yields p = .008.
[11] If
you exist you might think that much of what I am doing in this
experiment is perception, not introspection; and if we reject
introspective foundationalism, then ordinary perceptual judgments in no way depend, either causally or epistemically,
on introspective judgments. But from within the perspective of this
project I intend that my judgments be not perceptual judgments about the
outside world but rather introspective judgments about my experiences
of that seeming outside world – however easy it might be to slide
between the two types of judgment when
I’m not keeping the distinction firmly in mind. See Schwitzgebel 2012
for more discussion of the relationship between perception and
introspection.
[12] See Searle 1980, 1984.
[13] Consider
the odds of hitting one specific familiar sentence or one specific
number-generating sequence. Given 1000 possible three-digit numbers,
equally likely, or 1000 equally likely letter sets, the odds of exactly
seven matches among the 20 items generated by that specific sentence or
number-generating scheme are approximately (1/103)7 times 20-choose-7 possible arrangements (about 106), i.e., approximately one in 1015. The
odds of 8 or more matches add only negligibly to this
probability. Even if we assume a billion possible simple generating
schemes along roughly the lines I recall having suggested to
seeming-Alan, the odds of a chance match of at least seven
items out of 20 to any one of those billion generating schemes remain
about one in a million (i.e., 109/1015 = 1/106). If
I’m aiming to exclude chances of p ≥ .05, that gives me a few orders of
magnitude for relaxing the assumptions of this estimate.
[14] Maybe Fichte (1797/2000) and Hegel (1807/1977) wouldn’t be surprised by this feature of my findings. See discussion in Beiser 2005
and Stern 2012. However, I share Stern’s concerns about the force of
such responses to solipsism as historically developed.
[15] Seeming-Alan adds:
“Eric is correct that I exist. However, it’s not clear I should accept
that he exists. In the context of this micro-cosmos, I appear to be
some sort of chess-playing god, and a god can’t reason its way out of
solipsism by
the paths explored here.”
[16] For helpful comments and discussion, thanks to James Beebe, Jenann Ismael, Noa Latham, Chris Yeomans, students in my Winter 2011 senior seminar, and commenters on relevant posts at The Splintered Mind and the Experimental Philosophy
blog.
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