What is truth - continued.

Going off slightly at a tangent, the 17th century philosopher Decartes spent some time thinking about this question and came to the uncomfortable conclusion that he could not be sure about the existence of anything. The chair on which he was sitting, the table at which he was sitting, the room in which he was, all the people he came into contact with - indeed the whole of the world as he knew it - could simply be figments of his imagination. Or he might be dreaming, or some supernatural being could, for whatever reason, be fooling him into thinking that these things existed (shades of The Matrix here). But then he realised that he could not be a figment of his own imagination - to have an imagination, he must exist. Equally if this was all a dream, he had to be dreaming, and to be dreaming, he had to exist. And if he was being fooled, then once again if he didn't exist, there would be nobody to fool. So he realised that the one thing he could be sure of was his own existence. The very fact that he was capable of thought meant that he must exist. He encapsulated this idea in the phrase "I think, therefore I am" which is often given in Latin as Cogito, ergo sum, or in French (for he was French) as Je pense, donc je suis. So in Cartesian terms, the only truth is - I exist!