The External World: More Experimental Evidence of Its Existence

(collaborative with Alan Moore)

I’m engaged in a certain exercise. You might doubt the value of this exercise, but it’s a traditional philosophical exercise, and I’m a philosopher. The exercise is attempting to prove the existence of an external world beyond my own stream of experience.

As I mentioned in a previous post, the two most historically famous proofs of the external world appear to be unsatisfactory: Descartes’s because it turns on the dubious claim that the idea of perfection could only be caused by a perfect being, and G.E. Moore’s because it starts from the question-begging premise “here is a hand”.

My strategy is this: First, I assume introspective knowledge of my current sensory and other experiences, memory of past experiences back to the beginning of the exercise, and the general concepts and methods of science insofar as those are stripped of any presupposition of a world beyond my stream of experience. Then, I attempt to find experimental evidence sufficient to justify belief in a world beyond my stream of experience, as the best scientific explanation of patterns in my stream of experience.

In Experiment 1, I did something that seemed like programming a spreadsheet to determine whether various four-digit numbers were prime, and I also guessed whether those numbers were prime. As confirmed by subsequent hand calculation, the seeming spreadsheet did a far better job than I did at correctly marking the primes, and the best explanation appeared to be that something exists with calculating abilities exceeding my own – at least insofar as the “I” is conceived solipsistically, as constituted entirely by my stream of experience.

Experiments 2a and 2b:

Now I will try a second experiment, using an apparent confederate. I will call this apparent confederate “Alan”, though without meaning to presuppose that he exists as anything but a figment of my own stream of experience.

This “Alan”, by what I think of as prearranged instructions, gives me a list of 20 three-letter combinations to memorize (“EMA”, “GLL”, etc.). The list of three-letter strings appears orally, by which I mean that I seem to hear him say the 20 three-letter combinations. He appears to present the list twice. I then attempt to freely recall the letter-combinations from the list, offering up six guesses – the three-letter strings that it seems I can recall without prompting. “Alan” then presents me visually with a forced-choice recognition test: 40 three-letter combinations, half of which he says are new and half of which he says are the original 20, in random order. I select 20 of the 40 as my best guess as to which are the old ones. I feel high confidence about 10 of these guesses. We then repeat the same experiment with a second set of three-letter combinations. This time I offer up eight guesses in free recall and in the 40-item recognition test I again feel high confidence about 10 items.

Now, if nothing exists beyond my own stream of experience, then the forgotten items on these lists should not, it seems, be stable. They exited my mind – either as measured by free recall or by the stricter measure of recognition – and thus they exited the universe. Thus, when Alan seems to present me with these lists a second time, which he will shortly do, nothing endures across time that could anchor the forgotten items in place, ensuring that the new perfectly matches the old. The seemingly re-presented items could be any set of plausible items; my mind has unconstrained liberty to invent any letter combinations that seem reasonable candidates to span the gaps in my memory. On solipsism, the present needn’t preserve the details of the past; it need only preserve, seemingly can only preserve, the details of the past that I remember.

However, Alan now shows me evidence that undercuts this solipsist picture – evidence suggesting that the 20 three-letter combinations that were the “right” answers in each test were in fact anchored in place and stable across time rather than created at liberty anew. He shows me, first, the lyrics of “Take Me Out to the Ball Game”, and he tells me that the first 20 three-letter combinations were the letters, in reverse order, from the end of the chorus of that song (excluding spaces, punctuation, and two repeated letter combinations). As I look through that list of letter combinations (“EMA”, “GLL”, “ABD”, etc.), it is quite evident to me that this is the case: I am forcefully struck by the fact that the letter combinations that I do seem to recall from the original list fit exactly into that pattern, though I was entirely unaware of that pattern at the time they were originally presented. Comparing my free recall and recognition lists with the reversed-ballgame song, I see that 5 of my 6 freely recalled letter combinations appear in that song (one guess, Alan tells me, was wrong) and that 15 of the 20 I seemed to recognize were correct, including all 10 about which I felt confident in the recognition test. The other stimulus, Alan tells me, was similarly derived in backwards chunks from a sentence from George Berkeley: “In short, if there were external bodies, it is impossible we should ever come to know it; and if there were not, we might have the very same reasons to think there were that we have now.” Here, Alan tells me I accurately freely recalled 7 of the 20 combinations (having made one erroneous guess out of eight) and correctly recognized 16 out of 20, including all 10 about which I had felt confident.

Why should I believe that these lists now shown to me by this seeming Alan actually match the original ones presented? Their structure suggests so: Although I am not assuming the existence of ballgames or peanuts or cracker jack, it is one of the background assumptions of this exercise that I permit myself my existing conceptualizations, stripped of any commitment to a really existing external world. And my conceptual structure contains the song “Take Me Out to the Ball Game”, in which these words appear as indicated. Likewise, it’s part of my conceptualization of George Berkeley that this is just the sort of thing he would say and of Alan’s sense of humor that he would use this sentence to generate the stimulus. While it’s remotely possible that from the fragments that I happened to remember such natural-seeming structures could be found post-hoc to fit, that would seem to require enormous happenstance. Suppose that there were as many as a trillion possible strings of text Alan could have used, per the instructions I seem to remember having given him, to generate suitable test material, given present purposes. And suppose conservatively that English allows only about 1000 viable, roughly equiprobable, plausible three-letter combinations (it would be about 18,000 if all 26 letters could appear in any combination). Still there would be only about a one in ten billion chance that I could find two matches from that trillion strings for my two sets of ten confidently recognized three-letter combinations.

A better explanation, I venture, than such a boggling chance is that these remembered letter combinations were indeed generated in something like the manner described by this “Alan”, and thus that the lists Alan is now showing me do, as he says, match the original, in both their remembered and their unremembered parts. In other words, this pattern among my remembrances was not constructed anew but was present from the beginning in the original experience of hearing the letter combinations, including in the unremembered parts of that experience, since without those unremembered parts the strings would not fit the stated pattern. But then these lists, or at least the pattern they reflect, must have endured beyond my conscious ken from the time of original experience to the time at which the pattern was revealed to me, sustained by some mechanism running outside my stream of conscious experience.

Maybe my knowledge of the ballgame song or the Berkeley sentence operated nonconsciously in me to generate those letter combinations from the start? But that hypothesis still involves rejecting the most radical form of solipsism, the form of solipsism currently under discussion, which posits that all that exists in the universe is my own stream of experience. I don’t conclude that I know what, exactly, is beyond my experience – that Alan exists or that the physical list exists – only that something is beyond. That something might be my nonconscious mind.

Maybe my conceptualization of song lyrics and great philosophers is, unbeknownst to me, highly labile, so that although it seems that the lyrics are annoyingly familiar and the quote from Berkeley oh-so-apt, in fact this sense of familiarity and aptness arose wholly for the occasion, via some strange law of relating past and present experience, and the combinations are actually new, perhaps even the words themselves new English words? Then there need have been nothing outside my own conscious experience that endured from the first moment of presentation until now. This objection seems ad hoc given the background rules of this exercise, but in any case, it can be avoided with a third experiment.

Experiment 3:

Experiment 3 is structured much like experiments 2a and 2b, except that the items to be remembered are 20 three-digit numbers. So: I (and “Alan”) run the experiment. Alan tells me, now, that I have correctly freely recalled eight three-number combinations (nine guesses with one error) and have correctly recognized 15 items, including all of the eight combinations about which I felt confident during the recognition test. What suggests the stability of the list in this case? Alan tells me that the 20 three-digit numbers are actually the first 60 decimal places of the long cyclic number that comes from dividing 1 by 1939, the year in which G.E. Moore delivered his famous “Proof of an External World”. This time, instead of trusting in the stability of my conceptualization of song lyrics, I plan to trust to the stability of mathematics, confirming the list’s stability, the existence of the pattern Alan alleges to unite the initial and present stimuli, by long division by hand to 60 decimal places.

But, alas! After the first six digits something has gone wrong. Hand division does not confirm the list; the numbers diverge. Have I made a calculation mistake? No, evidently not, unless I am very deeply confused. Is there, perhaps, no external world or stability to mathematics after all? I suppose I am a biased experimentalist; I am reluctant to draw that conclusion. The number is a bit larger in the 7th digit, so on a hunch, I check the decimal expansion of 1/1938. Indeed, there is a perfect match all the way out to the 60th digit, between the list Alan tells me was the original stimulus and the hand-proven results of my calculation. (N.B.: In subsequent conversation “Alan” confirmed the diagnosis, but that small slice of experience is outside the scope of the experiment and thus out of bounds for now.)

I seem to recall having suggested to Alan that he use a long cyclic decimal expansion or some other readily calculated but unpredictable number string to generate the list for this experiment. Supposing that there were a million suitable pseudo-random number strings from which Alan might have chosen, the odds are over a million to one that all eight stably remembered three-digit combinations would appear among the 20 sets of three digits from one of those million candidate number strings. Again, the more likely explanation appears to be that the eight remembered combinations were indeed generated by the discovered pattern, along with the other unremembered combinations, and thus that the present list matches the original list and consequently that something endured over time, preserving that structure outside my conscious ken, contra the radically solipsistic hypothesis. This conclusion appears justified even though it took some searching to find the driving pattern.

Discussion:

The resolute skeptic will, of course, find joints at which to challenge this argument: Maybe the laws of math aren’t stable over time. Maybe there’s unmediated action at a temporal distance between my first oral experience of the list and my subsequent visual experience of the list. Maybe my memory is so poor that I can’t even trust that I did in fact recall several items correctly and this whole business has been an illusion of the past five seconds. In general, anywhere there is an undefended premise, the skeptic can insert a knife; and all arguments must have undefended premises on pain of regress. But recall the aim of this exercise: It is to provide experimental evidence, in the form not of incontestable proof but rather of inference to the best explanation, for the existence of something beyond my stream of experience, while taking for granted knowledge of my stream of experience and my pre-existing scientific standards and conceptualizations except insofar as those standards and conceptualizations presuppose the existence of anything beyond my stream of experience. That, I tentatively believe I have done.

Proposals for a fourth experiment warmly welcomed.