I just picked up the book "What does it all mean? - a very short introduction to philosophy" by Thomas Nagel...
In the third chapter - Other Minds - the author brings up the thought that we should assume our consciousness is the only thing that exists. If we make this assumption, then how can we explain this? How can we explain exactly what our thoughts are? Furthermore, how can we explain the fact that other people will assume the same thing (that theirs are the only existing thoughts, and I am some sort of non-existing thought form)?
If I assume that I have the only existing thought in my universe, then shouldn't the man who wrote this book - who agrees with the same assumption - have the same assumption: that HIS is the only existing thought ... which should prove that we both exist in relation with the same assumption.
(This can get really confusing to me as I am only 17 and don't know too much about philosophy yet, but can you please shed some light...)
You are right. If you and I each assumes that our own thoughts are all the thoughts there are, then we are both wrong. Of course if I am really the only thinker, then my assumption would be correct, but it does not look like I could justify that assumption, since if you were out there too, you would be in just the same situation as I am. The way out of this, I think, is to see that the point is not that I have reason to believe that there are no thoughts other than my own, but that my own thoughts are the only ones I can be completely sure about. However much experience and however many thoughts I have, it is still possible that there is nobody else out there. Of course we all believe (rightly, in my view!) that there are other people and their thoughts out there, but the puzzle you have asked about encourages philosophers to try to work out how we can know this.