Definitely got some good stuff here and in the other thread. Let me try to address three points here:
First,
Now, I’ve taken the Davidsonian route here, but you can also take the Wittgensteinian route and question the connection between dubtibility and knowledge. I’ll let that go for now, but I want to point out that this quote already presupposes his conclusion. Why did he decide that there are only two sources of knowledge? Why lump all five sense together and call it sense, why separate this from thinking processes? Why, in fact, call these sources, even separate sources, of human knowledge and not facets of a holistic human individual? Senses and reason aren’t sources of knowledge, they are what make us us. Do you see how the conclusion is foretold by the premises inherent in this quote?
It may seem like I’m being a little hard on the old French guy here, but that’s not really my intention. I think these basic Cartesian intuitions are still the default position for many, and while I probably won’t be able to persuade many people that there’s a better way to go, I might be able to modify this dualism just a bit and, as I said before, show that we aren’t cut off from the world at all. Of course, I suppose I haven’t done a very good job at doing that yet.
I’ll address your river source point later, but I see no inherent reason to confine ourselves to two abstract sources of knowledge and many good reasons to see many ways of checking and double checking what you call sources. To go back to the stick for example, how does Descartes know that his senses are deceiving him if he didn’t, I don’t know, thrust his hand in the water and find his sight misleading him. It seems very clear to me at any rate that he just could have accepted that something about the distinction between water and air changes the nature of the stick rather than the nature of his sight. Now, you’ll probably say that he doesn’t know that he’s being deceived, he’s only stating the possibility of being deceived – two different things – but my point would be that he knows that he can possibly be deceived. If he doesn’t work from that point, I don’t see how he can get any further than an endless, circular doubt.
Second, the dream hypothesis.
Ironically, those who propound this theory never seem to take it seriously enough. When you’ve been dreaming, most of the time you know your dreaming, but I accept the idea of lucid dreaming – a point for whatever reason where you really can’t tell the difference. I’ve been in one of those dreams where you wake up in the dream and given that it was a RipVanWinkel kind of dream, it was a rather frightening and dismaying experience. Yet, nevertheless, most of my beliefs remained intact, it was not a completely alien world, my wife was twenty years older but she looked the same (and she blamed me for sleeping for twenty years just as she blames me for many things I consider out of my control ), my daughter kept flashing between my picture of her now and my picture as she might be twenty years from now (much like it might happen if it, well, really happened). The point is that if this is a dream right now, it doesn’t change the fact that even in dreams most of your beliefs aren’t questioned. If they were, dreams wouldn’t be interpretable (both in and outside of the dream) and of course they are.
We might even say that the only thing being put into question is the dream/reality distinction. To which my answer is so what? I see nothing foundational to that distinction. That shouldn’t be surprising as I don’t see any particular belief as foundational, I see them as holistically coping with the world. Descartes search for a foundation is flawed because the very search for a foundation seems to me to be flawed, even incoherent when we try to assess the things we actually do to get around in this world.
Less than a hundred years ago we believed in a steady state universe, fifty years ago, we believed in an expanding but slowing universe, we now believe, or many do at least, believe in an expanding but accelerating universe. Is that really any more fantastic than the idea that we live in a dream?
And anyway, last time I checked reason doesn’t account for such things as quantum superpositioning or tunneling.
Third, Matrix.
Enjoyable movie with its flaws and religious overtones (Who exactly is the Oracle anyway?). Look forward to the sequels. But my argument remains much the same. Given the premise that we could be in a computer simulation doesn’t change the fact that most of Neo’s beliefs are still true, it is only the way he received them that is different. They speak English in and out of the Matrix, he has people to help him through the transition, people who are much like the people he met in the Matrix, he still has to eat, he can still fall in love, and perhaps most poignantly for any kind of narrative tension, if you die in the Matrix, you die in the real world.
It really isn’t as staggering as some may think. The effect isn’t a representation of Cartesian thinking so much as caused by Cartesian thinking. If I remember my Celtic mythology/literature class correctly, the idea of other worlds was more or less taken as a given. So a Celt would simply see this as a jump to a different world.
And wonder of wonders, I think it’s clear that Neo already knew something was ‘not right’ with the world. He actually suspected it, and I suppose that many who take this movie more seriously than I do also have that feeling. Contrary to incoherence or destabilization, they might actually feel slightly vindicated. But that just means that one of my beliefs was false, and one of theirs was true. But most of our beliefs in either world are still true.
A far scarier proposition is something like Putnam’s second Twin Earth paradox. There’s a twin earth on the other side of the sun, in all respects the same as this one with one difference suitably adjusted for. Water on this planet is always twenty percent grain alcohol. This doesn’t bother them as their body chemistries are different enough to account for that (and let’s say their science gives them no ability to tell the difference between our water and their water). You are spirited away without your knowledge to this planet and find you are always drunk. At what point, do you stop arguing with other people that they are wrong and start questioning your own sanity?
Most of your beliefs are still true, but you have no way to account for this, not because you are wrong, not because they are wrong, but because you have no way to explain the difference between you and them.
What kind of hell would that be?