I came across this statement on the Web earlier this week, and wondered about it, and decided to investigate more:
If there are multiple instances of the same document on the web, the highest authority URL becomes the canonical version. The rest are considered duplicates.
I read that article from Dejan SEO, and thought it was worth exploring more. As I was looking around at Google patents that included the word “Authority” in them, I found this patent which doesn’t quite say the same thing that Dejan does, but is interesting in that it finds ways to distinguish between duplicate pages on different domains based upon priority rules, which is interesting in determining which duplicate page might be the highest authority URL for a document.
The patent is: