If you ask an educated person about relative pronouns in English, you will hear a list of words starting with wh: who, whom, whose, which, where, whence, whither, why, when, whoever, whomever, whichever, wherever – and on occasions ‘what’, as well as ‘that’. There’s plenty of discussion among grammar nerds, English teachers and students of the language about when to use ‘that’ and even ‘what’ gets the odd mention when correcting sentences like ‘The book what you borrowed.”
Nobody adds ‘as’ to the list. Yet this little word has a respectable history as a relative pronoun among its many other functions, including usage by Shakespeare: “Fruits as maids call medlars“ (Romeo and Juliet, IIi). When experts discuss this line it’s usually to point out the pun. None of them, to my knowledge, has parsed it and remarked on the function of ‘as’ here.
How far back this usage goes I don’t know. Maybe there’s a doctorate in there for someone interested enough to pore through volumes of mediaeval and old English texts with a magnifying glass and the patience of Job.
It’s one of those things that has survived in the saying ‘Handsome is as handsome does’ meaning that only the person who acts in an admirable fashion is actually admirable. Everyone understands that saying, so it can be assumed that ‘as’ is still acceptable as a relative pronoun. And in fact it can be heard every day in uneducated speech and dialects: “Him as lives next door” “Her as killed her husband”. Is it just a simplification or mispronunciation of ‘that’? After all, the oral language came first, spelling later.
Them as knows the answer, please tell!