Thursday, January 05, 2012

Is Solipsism Simple?

Solipsism is the view that nothing exists but one's own stream of conscious experience. In The Problems of Philosophy (1912), Bertrand Russell says that although it's logically possible that solipsism is true, solipsism should be rejected as less simple than the hypothesis that an external world exists. But is realism about the external world really simpler than solipsism?

On the face of it, you might think solipsism is simpler. After all, it involves radically fewer entities. That's the great Ockhamesque beauty of it. Solipsism may be crazy, but at least it's simple!

Russell employs two arguments against the simplicity of solipsism. First:

If [a] cat exists whether I see it or not, we can understand from our own experience how it gets hungry between one meal and the next; but if it does not exist when I am not seeing it, it seems odd that appetite should grow during non-existence as fast as during existence (p. 23).
When human beings speak -- that is, when we hear certain noises which we associate with ideas, and simultaneously see certain motions of lips and expressions of face -- it is very difficult to suppose that what we hear is not the expression of thought, as we know it would be if we emitted the same sounds (p. 23-24).
Thus, he concludes, "every principle of simplicity urges us to adopt the natural view, that there really are objects other than ourselves" (p. 24).

Now, I'm inclined to think that Russell's argument here is very inadequate. But let me quickly say that I've found it surprisingly difficult to uncover what I'd consider to be better arguments against solipsism in the philosophical literature. Plus, Russell is famous! So let's take him seriously.

To see the core problem with Russell's argument, consider dreams. In dreams, cats can grow quite quickly hungry between appearances, despite their nonexistence in the interval. And the voices and faces seen in dreams reveal the real existence of no other independent mind. It seems no great violation of simplicity to suppose that, in a dream, the appearances of the cat and the voices and faces are concocted on the spot by me. No need to posit a giant, really existing universe, light-years upon light-years wide! And the solipsist, it seems, can just treat waking experiences the same way. Simple!

Russell is of course aware of dream skepticism, addressing it thus:
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 there really is a physical world (p. 24).
I think one might just as easily turn this argument on its head. If we assume solipsism rather than realism, we can invoke principles explaining why cats and people seem to behave as they do: They are imperfect projections of me upon my imagined world, based on what I know from introspection about myself. That theory is of course sketchy and incomplete, but so is the current scientific account of the content of dreams!

Now it might seem that postulating an external world behind appearances can at least explain correlations that must remain unexplained in solipsism. For example, if there is a real penny that I'm both looking at and manually rotating, the real existence of arm and coin explains why such-and-such changes in visual experience co-occur with such-and-such changes in tactile and proprioceptive experience.

I see two obvious replies for the solipsist:

First, why can't it simply be a law of my experience that such-and-such tactile and proprioceptive experiences will tend to co-occur with such-and-such visual experiences? Surely there's a theoretically discoverable structure to such co-occurrences -- a structure not so different, perhaps, and probably simpler, than that employed in the realist's account of tactile and visual perception and motor control and its relation to external objects. After all, realists' psychological theories, if they're really going to explain the relation among the experiences, require complicated overlapping and competing brain mechanisms for determining, among other things, visual shape and orientation from optical input.

And second, if simplicity really favors the theory with fewer unexplained coincidences, won't solipsism win hands down, even if it leaves a few things unexplained that the realist can explain? The small world of the solipsist will have vastly fewer such coincidences in total, and vastly fewer free parameters, than the enormously large, fine-textured, and richly populated world of the realist.


Anonymous said...

I have difficulty accepting that solipsism could ever be overturned by an inference to the best explanation of available evidence.

Descartes seems to have agreed with me: he does not infer in any methodical way from the nature of his sensory experiences to the reality of the corresponding objects. Instead he opts for something much more theological: his accepting the reality of external objects follows most essentially from his trusting relationship to God.

Anonymous said...

"...his accepting the reality of external objects follows most essentially from his trusting relationship to God."

I always found this bit strange. If solipsism is true, and realism is the wrong conclusion from the evidence, is the appearance of a cat without there being a cat really a deception on God's part? He's not responsible if Descartes keeps using his free powers of judgement to make faulty inferences the the existence of real cats. The assumption that if there appears to Descartes to be a cat then God owes him a cat amounts to an abdication of the epistemic responsibility to not make unwarranted inferences on Descartes part. And the assumption that any appearance of a cat has the role of pointing to a real cat, so that if it appears to Descartes that there's a cat and there isn't then he's suffered deception, possibly begs the question against the solipsist.

Carl said...

It seems to me that any attempt to create a "robust solipsism" eventually collapses into a distinction without a difference. If the cat is still getting hungrier when you're not looking at it, what's the cash value of saying it's not "really" there? Besides the one pointed out by Dinosaur Comics:

clasqm said...

Possibly an urban legend: Someone wrote to Bertrand Russell:

Dear Prof Russell, I want you to know that I am a solipsist. This philosophy has given me much comfort over the years, and I do not understand why more people don't become solipsists ...

Eric Schwitzgebel said...

Thanks for the comments, folks!

@ anon(s): I agree that Descartes' argument is weak, starting with the proof of the existence of God and continuing into the God can't be a deceiver part. This is part of what I meant in saying that good arguments against solipsism are hard to find.

@ Carl: The concern about the unconscious mind at the end of that cool comic is exactly why I define solipsism as the view that all that exists is one's own stream of conscious experience. If we can get from that to an unconscious mind, the external world follows soon enough, I think. But I don't think that the uncontrollability of one's experience establishes the existence of something outside of that experience. Various philosophers have made such remarks but rarely do they offer justification. There could just be laws intrinsic to experience, restricting the possibilities.

@ clasqm: I hadn't heard that one. Thanks!

Anonymous said...

Hey Anonymous2 - I'm the first Anonymous, so I'll go by Anonymous1.

I agree with your remarks on Descartes - and those are not the worst of his problems. I don't know that anybody can or does find the "epistemic theodicy" stuff (Meditations 3-4) persuasive in its own terms; it certainly looks self-serving, circular, and vague (at least to someone who thinks he lacks the requisite clear and distinct idea of God).

The point I wish to retain: Descartes accepted that solipsism was a problem that outclassed empirical ways of doing business. There is no such thing as concluding either for or against solipsism from the kind of sensory experience we have. That Descartes overcomes the hurdle with theological commitment rather than lucid argument indicates his assessment of the proper remedy.

The only philosopher who really satisfies me on mind-world relation is Kant, but I find that most discussions of the topic remain mired in what he would call "transcendental realism" - including discussions about him, which therefore look very confused to me.

Pete Mandik said...

@Eric & @clasqm:


Eric Schwitzgebel said...

Thanks, Pete!

Anon1: I think the empirical approach can be done better, though not entirely without making some assumptions that the solipsist might regard as unjustified. One attempt is Alan Moore's & my blog post from June:

I also agree that there are merits to a broadly Kantian picture.

TUM said...

Wasn't it Russell who also turned the tables, and said omething like this. Without some evidence for it's truth, why should Solopsism even be considered? I mean, I could equally postulate the existance of Unicorns. They're just invisible. And Massless. And really good at not being bumped into. It would be very hard to prove me wrong, but what use is my theory?
I see Solopsism in much the same way. It may be hard to get rid of, but as long as there are more useful alternatives, there is no reason it should be prefered.
Still like your thought experiments though.

clasqm said...

@ TUM: Come on, it's too early in the year for the annual verificationism vs falsificationism food fight ...

Alan Moore said...

Quine has a short piece on simplicity in "The Ways of Paradox" called "On Simple Theories in a Complex World." Did I say it was short? He claims that simplicity is relative to a conceptual scheme, so something could be simple on one scheme and complex on another. For Quine, "simplicity" is not an objective property of a theory.

We see something like this in logic. Can't we get a complete logical system using the sheffer stroke as the only connective? Simple. Yet what a pain to translate in and out of english. Not simple.

And the same happens in metaphysics. I have a hazy memory of Michael Jubien arguing for a simple ontology: no relations, just properties and sets. Yet as an undergrad, this sounded horribly complex. Abstract objects - I wanted the simplicity of empiricism.

I find measuring simplicity to be even more difficult than measuring distance between possible worlds!

Eric Schwitzgebel said...

"From the simple assumption that Star Trek is true, much of interest follows" -- John Holbo, UC Berkeley grad student lounge circa 1994.

Simplicity relativism sounds good to me. The case against solipsism needs to be built on different grounds.

clasqm said...

"From the simple assumption that Star Trek is true, much of interest follows" -- John Holbo, UC Berkeley grad student lounge circa 1994.

And he was right! The philosophy of popular culture is a growth industry.

Nightvid said...
This comment has been removed by the author.
Nightvid said...

Most modern philosophers of science (I suspect) subscribe only to a version of Occam's Razor which says you should minimize the number of postulates your theory is built upon, not the number of "things" being posited. Thus, solipsism is no simpler than non-solipsism, because you are positing, instead of X, Y, and Z existing, the *appearance of X*, appearance of Y, and the appearance of Z existing.

The reason I reject solispsism is that, in addition to being no simpler than non-solipsism, it lacks explanatory scope. Simplicity isn't the only criterion in evaluating explanations or competing hypotheses. For instance, if solipsism is false, it explains why it sure *seems* as though you gain a lot by distinguishing between what you know and what is true even though you don't know it, but find out later. Solipsism would require additional ad-hoc assumption to include that in its explanatory scope. Similarly with the apparent similarity between you and other people. Either you posit that you should get the right answers to all observables if you posit an approximate symmetry between you and other entities that appear to be people, or you don't. If you do, then your mind would have to have an infinite amount of nested seeming operators (i.e. to me it seems as if to her it seems as if to him it seems as if to...) to explain ANYTHING at all. If you don't, then you are still left with the apparent similarity between what seems to be you and other people completely unexplained.

So I think a compelling argument against solipsism can be made on the grounds that it is not simpler and lacks explanatory scope, or if you add to it enough to recover explanatory scope, it turns out to require more axioms and thus violates Occam's Razor.

These arguments would fail if you attempted to apply them in dreams because you don't really experience a world that behaves "normally" even though it doesn't bother you at the time (with the exception of lucid dreaming). If I am dreaming and close my eyes in the dream for a few seconds and open them again, I either wake up or the world completely changes into something different. This is very much unlike waking experience and it is easy to tell, *if* you want to and try to (which you usually don't). I would even argue that the fact that there *seems* to be a way to tell if you're dreaming or not is iself evidence against solipsism.

Eric Schwitzgebel said...

Nightvid: Thanks for that interesting, thoughtful comment! A few thoughts:

* I'm not sure we should acquiesce in the view that number of entities is not a major dimension of simplicity, even if that is currently the majority view.

* I agree with your thought that solipsism has trouble explaining the natural-seeming distinction between what you know and what is true even though you don't know it. In fact, that is the main feature of my own attempts to build a case against solipsism in collaboration with Alan Moore in a couple previous posts. And also like you, Alan and I emphasize the apparent ad-hoc-ness of the solipsist's countermaneuvers (though I'm not sure ad-hoc-ness and failure of simplicity are the same thing).

* I also agree that dreams probably lack the kind of stability that helps make the case, for the real world, against solipsism. For example, Alan's and my prime-number-guessing test (in a June 2011 post) probably wouldn't seem to play out correctly in a dream unless the dream also involves tricks of memory.

But let me conclude with the thought that it's not entirely obvious how to build the kind of philosophy-of-science-ish case against radical solipsism that you and I are talking about. My review of the literature is very incomplete, but so far I have seen nothing that I think really does it adequately. (If you have further suggestions, of course they would be welcome!) That's why Alan and I think we might have something novel to contribute.

Unknown said...

I have determined that you will read this as you have just inevitably done.
Therefor I know that you exist.

Eric Schwitzgebel said...

Hi, Roy, this is your unconscious mind. Eric Schwitzgebel, and all other apparent people, are simply figures of your/my/our imagination.

Unknown said...

Nevertheless, you've postulated a reliable form of predictable existence.

Aleksander Więckowski said...

Dear Eric,

I thought you might be interested to know that as an answer to this year's Edge Question: "What is your most deep, elegant or beautiful explanation" Thomas Metzinger wrote an essay titled "Simplicity itself", devoted mostly to Ockham's razor.
I wish I could see him confronting your fantastic post:)

Eric Schwitzgebel said...

Aleksander, thanks for the tip. I'll check it out!

grace said...

I am currently researching for an essay on the mind body problem, i,ve read descartes theory along with berkeley and russell, I came across solipism by chance and tho' I do not profess to be a philosopher, having been studying the subject less than 6 months,I find descartes arguement weak and inconclusive and this seems to be the strongest challenge to decartes theory. I cannot say with full conviction that I accept it as my stand point, but it has a very strong arguement and one you present with extreme reason.

Eric Schwitzgebel said...

Thanks, Grace!

supersmart said...

Yes solipsism is simple, and that we don't know there's an external world is simpler than saying "there's an external world", but methodological solipsism is complicated and not so simple. I have to therefore draw the conclusions of my senses (touch, taste, feel, smell, sight, and hearing), and focus only on that, together with Ockham's razor, and use no induction, and conclude I may be a brain in a vat, which isn't simple, but if I said you don't exist and you're zombies, together with disbelieving in God's existence and not doing moral codes it's as simple as that: each element isn't subdivided, and to say there's an external world I would need an explanation of the unperceivable, that someone did something I can't see or touch is the case, with no logic and no proof, wouldn't be so simple as solipsism, but given my logic isn't simple, it's simply the case of my senses and not believing anything I can't sense, being unknowable as to whether it's a hallucination, it's simply the case that there's no gods.

Eric Schwitzgebel said...

Yes, simplicity is a complex business!