Solipsism is one of those fetid intellectual dark alleys that some people just can't resist walking down. I never saw the appeal myself, I enjoy having friends too much. Eventually most people turn around and head back toward the light. Nevertheless, there are still too many who think it's pretty deep stuff. If you find them as annoying as I do, you might be in the market for a fast, comprehensive smackdown. Here it is. Or, you could just pinch them till they cry.

If the following is of little interest to you, just skip ahead to the next part for something completely different.

Solipsism is usually defended only as a means of attacking scientific reasoning, or as a stepping-stone to one of its many variants. By the same token, a good way of defending science against a variety of criticisms, and of understanding the true relationship between reason and reality, is to consider the argument against solipsism.

There is a standard philosophical joke about a professor who gives a lecture in defense of solipsism. So persuasive is the lecture that as soon as it ends, several enthusiastic students hurry forward to shake the professor’s hand.’Wonderful. I agreed with every word,’ says one student earnestly. ‘So did I,’ says another. ‘I am very gratified to hear it,’ says the professor. ‘One so seldom has the opportunity to meet fellow solipsists.’

Implicit in this joke there is a genuine argument against solipsism…[snip]…this argument is trying to show that solipsism is literally indefensible, because by accepting such a defence one is implicitly contradicting it.

But our solipsistic professor could try to evade that argument by saying something like this: ‘I can and do consistently defend solipsism. Not against other people, for there are no other people, but against opposing arguments. These arguments come to my attention through dream-people, who behave as if they were thinking beings whose ideas often oppose mine. My lecture and the arguments it contains were not intended to persuade these dream-people, but to persuade myself – to help me to clarify my ideas.’

However, if there are sources of ideas that behave as if they were independent of oneself, then they necessarily are independent of oneself. For if I define ‘myself ’as the conscious entity that has the thoughts and feelings I am aware of having, then the ‘dream-people’ I seem to interact with are by definition something other than that narrowly defined self, and so I must concede that something other than myself exists.

My only other option, if I were a committed solipsist, would be to regard the dream-people as creations of my unconscious mind, and therefore as part of ‘myself’ in a looser sense. But then I should be forced to concede that ‘myself’ had a very rich structure, most of which is independent of my conscious self. Within that structure are entities – dream-people – who, despite being mere constituents of the mind of a supposed solipsist, behave exactly as if they were committed anti-solipsists. So I could not call myself wholly a solipsist, for only my narrowly defined self would take that view. Many, apparently most, of the opinions held within my mind as a whole would oppose solipsism.

I could study the ‘outer’ region of myself and find that it seems to obey certain laws, the same laws as the dream-textbooks say apply to what they call the physical universe. I would find that there is far more of the outer region than the inner region. Aside from containing more ideas, it is also more complex, more varied, and has more measurable variables, than the inner region.

Moreover, this outer region is amenable to scientific study, using the methods of Galileo. Because I have now been forced to define that region as part of myself, solipsism no longer has any argument against the validity of such study, which is now defined as no more than a form of introspection. Solipsism allows, indeed assumes, that knowledge of oneself can be obtained through introspection. It cannot declare the entities and processes being studied to be unreal, since the reality of the self is its basic postulate.

Thus we see that if we take solipsism seriously – if we assume that it is true and that all valid explanations must scrupulously conform to it – it self-destructs.

How exactly does solipsism, taken seriously, differ from its common-sense rival, realism? The difference is based on no more than a renaming scheme. Solipsism insists on referring to objectively different things (such as external reality and my unconscious mind, or introspection and scientific observation) by the same names. But then it has to reintroduce the distinctions through explanations in terms of something like the ‘outer part of myself’. But no such extra explanations would be necessary without its insistence on an inexplicable renaming scheme.

Solipsism must also postulate the existence of an additional class of processes – invisible, inexplicable processes which give the mind the illusion of living in an external reality. The solipsist, who believes that nothing exists other than the contents of one mind, must also believe that that mind is a phenomenon of greater multiplicity than is normally supposed. It contains other-people-like thoughts, planet-like thoughts and laws-of-physics-like thoughts. Those thoughts are real. They develop in a complex way (or pretend to) and they have enough autonomy to surprise, disappoint, enlighten or thwart that other class of thoughts which call themselves ‘I’.

Thus the solipsist’s explanation of the world is in terms of interacting thoughts rather than interacting objects. But those thoughts are real, and interact according to the same rules that the realist says govern the interaction of objects. Thus solipsism, far from being a world-view stripped to its essentials, is actually just realism disguised and weighed down by additional unnecessary assumptions – worthless baggage, introduced only to be explained away.

Hah! If that doesn't shut them up, nothing will.

You've been reading an excerpt from The Fabric of Reality, a splendidly thought-provoking little book by David Deutsch, which I highly recommend.

All of the above is a mere warm-up, heading towards a proof that the universe is in fact knowable. From there, it proceeds to advocacy of the many worlds interpretation and the existence of a much larger multiverse. Dr. Deutsch is a pretty interesting guy. Or perhaps he just has interesting interests.

Not long after September 11th, John Brockman's Edge Foundation asked the question "What Now?". Here is (in part) David Deutsch's response. I took the liberty of boldfacing a few little bits...

What happens now is that we (by which I mean the West) eradicate state-sponsored terrorism. And we can achieve that only by replacing all political systems that perpetrate or collaborate with terrorism, by systems that respect human rights both domestically and internationally.

This will require, first of all, war. Then, it will require spectacular success at the notoriously difficult task of improving other nations' political systems. But we have done such things before: we did it for Germany and Japan in 1945. We have also failed many times at it. We must succeed this time.

But more: it will require changes in us. In our conception of the political landscape. It will take violations of old taboos and the creation of new understanding and new traditions. Genuinely this time, it will require the creation of a new and better world order...

...mainstream Western culture has also exhibited a major moral failure: a refusal to distinguish between right and wrong. The unique glories of our civilisation — self-criticism, tolerance, openness to change and to ideas from other cultures — have in many people's minds decayed, under this moral failure, into self-hatred, appeasement, and moral relativism...

Moral relativism always sees itself as evenhanded, and indeed it begins with a retreat from judgement or taking sides. But in practice it always entails siding with wrong against right. I said that we need to change. Here is something that desperately needs to change.

A colleague wrote recently: "Despite the morality of responding in self-defence to a terrorist attack, I am thinking about how to find solutions that do not include tit for tat." Yet nothing that the West has done so far, or has threatened to do, or has proposed to do, has involved any hint of tit for tat...In reality, the impulse for revenge plays no significant role in the political culture of the West. If it did, then the vast, peaceful, humane and diverse civilisation of the West itself would not be possible.

It is not true that the recent attacks on the US were motivated by a state of mind similar to that which is currently motivating the Western response. The Western stance — and even Western mistakes, including appeasement and moral relativism — are driven fundamentally by respect for human beings, human choices and human life...

In contrast, the West's anger, and the West's restrained, careful and humane response in self-defence, are justified. The problem is not to find alternatives to defending ourselves against murderers. The exact opposite is true: this violence will end if and only if we defend ourselves, effectively...

You can perceive our stance and theirs as symmetrical only by expunging morality from your analysis: seeing all political objectives as being legitimate, all rival value systems as matters of taste, treating murderers and their victims with evenhanded sympathy...

You have to pretend that the richness and diversity and creativity of our civilisation are playing the same role in our lives as empty repetition, oppression, and pitiless enforcement of a monoculture play in theirs.

People wring their hands and say that there must be "better ways of finding solutions" than warfare. Of course there are. We have already found them. The nations and people of the West use them all the time. They are openness, tolerance, reason, respect for human rights — the fundamental institutions of our civilisation. But no way of finding solutions is so effective that it can work when it isn't being used.
And when a violent group defines itself by its comprehensive rejection of all the values on which problem-solving and the peaceful resolution of disputes depend, and embarks instead on a campaign of unlimited murder and destruction, it is morally wrong as well as factually inaccurate to represent this as a case of our needing "better ways of finding solutions"...