Deryk Barker on "transposing instruments":

>I gather from the Oxford Dictionary of Music that many clarinetists today
>use the Bb for both Bb and A parts, transposing mentally.  I trust they
>wouldn't try and play Eb parts this way, as the different instruments have
>different charecters and a fine orchestrator (Mahler for instance, who was
>very fond of the Eb clarinet) will exploit the fact.

Vaughan Williams used to complain about writing for the Eb clarinet,
although he didn't often do without it.  He writes in a letter to, I think,
Roy Douglas (his amanuensis), that he "never has gotten the hang of"
transposing for the Eb clarinet.  Apparently, he'd forget he was using the
Eb and transpose as if for Bb or A.  For this and many other reasons,
Vaughan Williams's manuscript scores, deposited in the British Museum (I
saw them on display in 1972), should not be considered definitive.

Steve Schwartz