Sadr: I think you can get a full explanation by googling. In short, I believe that it has to do with the history of the language in England. Many years ago, in some parts of England, some people used "s" for the third person, such as

Vincent, With my previous post I wanted to draw your attention to the fact that you're repeating over and over the same sentences. I am not sure in what way this helps you improve your English. How come you're still focusing on the same

on 06 Nov 2003: You're over-thinking this, or something. Subordinate clauses in English that ... when satellites are in a lower orbit." "When pigs fly." I agree with all of that, and I was aware of the common idiom when I wrote