Thorn and Edh in OE

[David L. White]

        'Tis a minor matter, but it is not true (as was pointed out long ago
by Stockwell and Barritt in their rejoinder to Hockett), that in OE thorn
and edh are used indiscriminately.  The general pattern (which unfortunately
is not strong enough to be a rule) is that thorn is used initially and edh
is used after vowels.  (Usage vacillates even more than usual in
environments not captured by one of these formulations.)
Even Kuhn, a veritably rabid anti-Hibernicist generally, was forced to
admit, soto voce, that this distribution probably reflects influence from
Irish spelling, where a distinction between intial and post-vocalic
environments is usual (and for various obscure reasons necessary).  It
appears that the original rule was to use "th" initially and "d"
post-vocalicaly, and that when thorn and edh replaced these, they inherited
this distribution.
        The odd thing is that in Irish post-vocalic "d" should, under
ordinary circumstances, spell /dh/, not /th/.  But cases like "peccad"
versus "peccath" show that there was some confusion on this point.  It seems
that, in final position, "d" was accepted as a spelling for /th/ in Irish.
This is made more likely by the fact that the "d" spellings are younger,
which would, if taken literally, indicate that the opposite of final
devocing had occurred.  Given the example of other languages, this does not
seem likely.