I was under the impression that old English manuscripts did use different
glyphs for the two sounds of th.
Not that I am aware of.
The two sounds normally indicated by _th_ in modern English were spelled interchangeably with thorn (_þ_) and eth (_ð_) in Old English and often in Middle English. This was just a change in spelling convention. All the spellings are representable in Unicode.
Thorn in later Middle English assumed an open-loop form which was close enough to _y_ to be confused with it, hence, when thorn as a letter in itself was forgotten, it was for a time still customary to spell _þe_ as _ye_ instead of _the_.
As to _gh_, corresponding Middle English words normally used the letter yogh (_ȝ_). The difference is in spelling. Both spellings are available through Unicode.
Jim Allan
