commit: fb200d8 - #595 (2014-04-14 00:44:57 -0400)
After Rand introduced this concept in a Whiteboard Friday last year, co-citation firmly took its place as one of the buzz terms for 2013.
There seems to be a general feeling that authority can be built with co-citation, but for me that's just not possible.
If co-citation was to pass authority, then the web would open itself up to huge amounts of spam again (nofollow is redundant in co-citation). People could comment with just a brand name or unlinked URL without throwing up any red flags. And Google is not at the point of understanding context/sentiment well enough to judge these citations.
So I want to discuss the actual importance of co-citation in Google's ranking algo. For me, we're just talking about 'off-page relevance' and nothing to do with authority; but perhaps others disagree?