Quote: Archibald A. Hill (maybe)

"A speaker of the language should be able to pronounce correctly any sequence of letters that he may meet, even if they were previously unknown, and secondarily, to be able to spell any phonemic sequence, again even if previously unknown." -Archibald A. Hill, distinguished U.S. linguist.

I have not been able to confirm the source. A google search reveals only two pages that mention the quote. Even if it is a misquote, is it still a good principle.