Rene Descartes' most fundamental work was his
Meditations. In these
he works to beat the
skeptic at his own game: there
is
something that is
knowable. The question then becomes what is
truly
knowable.
Is what I remember reliable?
unfortunately not. We all have memories that are wrong. At times
two people can sit there arguing about the color of a shirt years
ago. They can't both be right. Even our recent memories can be
drawn into question.
What about what the future? Is there anything trustable there?
Still no. We are constantly surprised by what happens in daily
life. How can we ever trust that something will happen?
Do I know that what I see is really there?
Nope. I see things in my dreams that are just as real
as the things that I see now. I could be still dreaming. It
is impossible to tell if I am dreaming or not... I could build
a device that tells me if I am dreaming or not, but then, I could
build that device in a dream and have it give me the wrong answer
just as easily.
So, we can't trust our senses for anything that we are to know,
but can we trust the basic foundations of math and logic?
Once again, nope. There could be an evil demon, or more modernly,
I could be a brain in a vat. Every time I think "1+1" I get the
answer "2" put into by brain by something, even though this isn't
right, because "1+1" is actually "3". Though, being a brain in
a vat, I can't help but think it when it is forced into my mind.
So we don't know that true is true, and "1+1" is "2", what can
we know?
Despite the fact that basic logic and our senses are not reliable, there is still something that is knowable. I am thinking.
From this, it is impossible for that to put into my brain sitting
in a vat without having a mind. There is no way to make a person
disbelieve that they exist. I think therefore I am. This is
an undeniable truth. I know this. I have beaten the skeptic.