I'm interested that nobody past the first post in this thread mentioned the long-lamented 'ye'. Back in Middle English, the second person singular was (nominative, objective, genitive, possessive):
thou, thee, thy/thine*, thine
* similar to a/an which persists today
and the plural forms were:
ye, you, your, yours
(The sounds have changed a bit too, so I'm simplifying a bit.) Some time around King James, 'you' began its great levelling of the second person when it took over the nominative plural, changing that form to
you, you, your, yours
This was also the correct form for addressing a singular person who was your social superior, as in most of the other western European languages. In English, though, the use of 'thou/thee' fell completely out of favour for no apparent reason.
Amusingly, in modern usage, 'you' used generically means, almost invariably, the singular form. Think about it; if you're addressing a group, would you say, 'Do you want to go to the rink?' When I do it, I usually wind up saying, 'Do you guys want...' or 'Do you all want...' Or is this just a Canadianism?
Also somewhere along the way the use of 'mine' before a vowel, instead of 'my', fell out of favour. Why did it happen? It just did. Languages mutate, just like genes do. There doesn't have to be a reason, and usually there isn't.
--
Trevor Green
"Military justice is to justice what military music is to music."
