To: Simon C.
From: Geoffrey Klempner
Subject: Wittgenstein on solipsism
Date: 1st November 2011 11:51

Dear Simon,

Thank you for your email of 23 October, with your first essay for the Philosophy of Language program, entitled 'Wittgenstein's World' on proposition 5.62 of the Tractatus: The world is MY world: this is manifest in the fact that the limits of LANGUAGE (of that language which alone I understand) mean the limits of MY world.' -- You were asked whether you agreed with this statement.

I like the strategy you have adopted for this essay, of first considering the statement 'as it stands', outside the context of the Tractatus and what we know/ believe Wittgenstein was trying to do; and then within the context of Wittgenstein's argument in the Tractatus.

In my comments I will follow your plan. Let's take as read the possibility that an AI could be constructed. The standard story is that our AI is an embodied computer interacting with our world and with us. However, in your version of the story the 'world' in question is a virtual reality (as in Doom or The Matrix), and moreover the subject who is aware of, say, the Matrix as a world is itself a computer generated object in that world (e.g. in the film, the AI program called 'Smith').

I count (at least) two programs here, although you, a software engineer, would be better placed to say whether or when one can draw the line between one program doing two tasks and two separate/ separable programs (crude example: MS Office). The important point is that Smith, say, alone in his 'world', has no knowledge of how he came here or how he world came to be, is ignorant of the fact that he and his world are merely 1s and 0s.

However, let's suppose that Smith is sufficiently intelligent to conceive of this possibility. 'Suppose I am...!'. To make that supposition, he has to reject the idea that 'my world is the only world'. His 'doom' is not solipsism but scepticism. It's a variation of the 'brain in a vat' scenario.

(Incidentally, there's an interesting thread on an answer I wrote for my Tentative Answers blog on solipsism: see http://tentativeanswers.blogspot.com/2010/09/definition-of-solipsist.html )

So we come to Wittgenstein. The first thing we have to put right out of the way is the idea that Wittgenstein's argument for solipsism relies, as you suggest, on the connotations of the term 'experience'.

It is true that Wittgenstein read Schopenhauer in his youth, and so was familiar with Kantian themes (such as Kant's 'Refutation of Idealism' and the idea that we can reconcile transcendental idealism with empirical realism). The world as I experience it necessarily is as it would be if there were objects situated at different spatial locations. In fact, there is no other logically possible way in which experience can be described. There's a strong echo of this at Tractatus 5.64 'The self of solipsism shrinks to a point without extension, and there remains the reality co-ordinated with it.'

However, Wittgenstein seems to offer an argument which is independent of the Kantian analysis of experience, one which relies purely on considerations of what it is for a proposition to have a sense.

You state, 'In the Tractatus Wittgenstein builds a world based on objects that are magically linked together by inexpressible laws of logic to form facts or possibly propositions.' What is 'magical', or necessarily inexplicable, is the fact that the facts are as they are, and not some other way. Any explanation would itself be a fact, which leads to infinite regress.

However, that the world is necessarily 'based on objects', isn't a fact because it is the conclusion of (what claims to be) a logically valid inference. Propositions have a sense. Whether or not a proposition has sense cannot depend on any fact, because we must be able to determine the sense of a proposition -- what it says -- independently of knowing what the facts are (echoes of Russell's theory of descriptions). Therefore, there must be something which all logically possible worlds have in common, something which exists in every possible world: objects and the possibilities of their combination. (There's an echo of this in Kant too, in his argument for the necessity of a spatial framework, and for the necessary existence of 'substance'.)

But whose language are we talking about? That issue hasn't even been addressed. Why must it be MY language?!

If it is necessarily 'my language' then we are home and dry. The situation cannot be as in our previous Smith scenario. Smith ponders the possibility that 'I may be an AI program running inside a virtual reality inside a computer' and those words make sense. Remember, Smith is not a solipsist. He hasn't read the Tractatus.

You offer a possible argument that Wittgenstein might have used. I don't think it gets to the crux of the issue. Why (as in premiss 2) is the language I am using a language which 'only I understand'? Why can't you understand my language? You're doing so now!

I think the crucial step is where Wittgenstein defines meaning in terms of rules (he talks of 'rules of projection' in the context of the picture theory). Whose rules? They can only be my rules, because there is no structure there to explain how I could be following rules which others follow also. There's no way, given the way the argument is constructed, to get outside the perspective of the solitary language user.

True, there is also no way to state the properties of GK which would imply that GK is 'unique', because the only things that can be stated are facts, and the only facts that exist are facts about the world, in which GK is just one living subject or agent amongst others. It can only be shown. The entire argument of the Tractatus shows it, in demonstrating that the conditions which Wittgenstein lays down are jointly necessary and sufficient for a proposition to have a meaning.

As you state, it is in the Investigations that Wittgenstein subjects this claim to a thoroughgoing critique. His conclusion: following a rule is a 'practice' which presupposes the existence of 'forms of life'.

All the best,

Geoffrey