MMario (your post 30 Oct 10:54am), and Stilly Rive Sage (your post 30 Oct 02 05:10pm): I don't think the history of the English language permits the belief that "you" developed from "thou" by a misreading of the thorn character. In Old English (aka Anglo-Saxon, spoken by Germanic settlers in Britain from C5 to C11 approx) the 2nd-person personal pronouns had 3 forms by number, distinguishing singular, dual and plural (as I understand Welsh does? but I'm no expert on Welsh - come to that, I'm no expert on English, either, but can read text-books as well as any man), as follows. Since I don't know how to get HTML to put a horizontal line over an "e", "i" or a "u" to make the vowel-sound that echoes the letter's pronunciation, I use acute accents; g is pronounced "y" approx - I won't go into voiced velar fricatives or palatal fricatives - and I represent the thorn character by an italicised th, thus: th.

Nom & Voc sing: thú (whence thou)
Nom & Voc dual: git
Nom & Voc plural: gé (pronounced "ye" approx, "O ye of little faith")
Acc Sing: thec, thé
Acc dual: inc, incit
Acc plural: éowic, éow, íow (the middle one is "you" approx, and not a thorn in sight! éowic is early and was replaced later by éow)
etc etc - no need to go further.

I live in north Derbyshire (UK), where the familiar 2nd-person singular may still be heard - particularly in pubs (is that because alcohol tends to remove the veneer that years of listening to the BBC have imposed, and makes us revert to childhood speech patterns?) - though in a very degenerate form. Oddly enough, the mainland Europeans, of whom we have a constant succession staying, and who I always try to introduce to "the pub", and who have such a (less degenerate) form, seem to be incapable of hearing it, even when I point it out.