Σκέφτομαι, άρα...

Philosophers are strange folk. They ask strange questions. Like "does this table exist?". Then they think about it really hard. For years. And then they decide they didn't like the question, and instead ask "What does it mean to exist?" and "What does it mean to be a table", and so on, for a few more years. That's why they have such long beards.

Anyway, they realised early on (after a few thousand years of thinking about it) that it was impossible to disprove the theory that you are the only person who exists. Everyone else and everything else is a figment of your imagination. Apparently the only people who believe this are insane, since if you do believe it you go mad. Or end up becoming a philosopher.

The internet raises these sorts of questions. I "know" people online, but I've never met them. They may not actually exist. Someone could be running a very clever computer program. In fact, it could be running on my computer. Or in my head. I've not got any way of telling. Is there really anyone there?

Bertrand Russell said that in the book "Principia Mathematica" which he co-wrote with Whitehead, there were passages which he didn't understand, which Whitehead had written, and that he couldn't believe that they could have come from his brain. Similarly a lot of the stuff spouted by my internet friends and acquaintances couldn't possibly have come from my head - surely? I'm not that sick? Am I? Now I can understand why all those people went mad. If I really believed that it was all my invention, I'd book myself into a mental home straight away.

James Boswell told Samuel Johnson about the idea of the non-existance of matter, and how it was impossible to refute it:

...Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it 'I refute it thus' [The Life of Samuel Johnson, 6th August, 1763]

Now why didn't I think of that? So I think that convinces me that stones exist, but I'm still not totally sure about you lot...