Empty Table Ruins Query

My goal is to create a query that selects authors that are NOT associated with a certain article. This would include authors that are not associated with any articles.

Here are my tables:

AUTHOR
id
first
mid
last

ARTICLE
id
title
body

ART_AUTH (link table)
artid
authid

Here is my query thus far:
SELECT author.id, author.first, author.mid, author.last, FROM author, art_auth WHERE author.id<>art_auth.authid OR (author.id=ar
t_auth.authid AND art_auth.artid<>$artid)

It works GREAT until the link table is empty. Then it returns 0 rows. In that case, I would like it to just return all the authors in the authors table. Have any sugestions???