"If you agree that there is a hand, we will grant you all the rest..."
From the tiny book "On Certainty" by Wittgenstein. Really interesting and thought-provoking.
From the tiny book "On Certainty" by Wittgenstein. Really interesting and thought-provoking.
TL;DR:
Descartes (and others): We can't know for certain that the external world exists.
GE Moore: "Here is one hand, and here is another. There are at least two external objects in the world."
Wittgenstein was pointing out that this doesn't address any of the actual claims. (I think "agree" is a confusing word to use in the translation. "Know" would work better.)
EDIT: I'd also like to throw this Moorean SMBC sub-comic because I love it and it's relevant: https://www.smbc-comics.com/comics/20100512after.gif -- from https://www.smbc-comics.com/?id=1879
Here is one hand,
And here is another.
There are at least two external objects in the world.
Therefore, an external world exists.
That is a good question. One possible answer would be "It depends on the quality of the simulation". If we are living in a simulated world there could be a simulated drug the so-called red pill which allows you to see the execution of the simulation.
If we started seeing Fortran source-code in the sky and the code would seem to be about running a world-simulation, and we would also see data-expressions in the sky that curiously described the world we experience outside of us then I think we would be pre-disposed to think it looks like we are simulated beings in a simulated world.
Held together with Perl, don't forget. https://xkcd.com/224/
Moore's point is: why is the internalist assumption any better than the assumption that here is one hand?
If there is a hand then everything else falls out deductively. Using induction, it's trivially true that there is a hand.
Using deductive reasoning to prove an inductive proposition is ultimately a waste of time, using inductive reasoning to create a correct framework for deductive reasoning is ultimately unknowable. Both of these together is how we live our lives and create our standard model, which is ultimately imprecise at best, and wrong at second best.
This is Moore's point, that we are wasting our time trying to deductively prove the existence of an external world when it's trivially provable. We may not get accurate axiomatic framework, but we can never get that anyway.
Much of the point of philosophy is properly delineating between these two methods of reasoning. Much of analytic philosophy is finding areas where language blurs the two.