How Google treat subdomain and root domain?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Eva Brown: Actually, Google treats the sub domain as a separate website. Now tell me if I get a backlink to another website other than mine, will my website rank? No. So, what can I do? There are two ways. One is directly create a backlink to your root domain or where article is published. Other ways is, you can interlink both domain so that link juice will pass from one to another.
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  Jeremy L. Knauff: No. Google does not treat sub domains as separate websites.
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  Eva Brown: Actually yes, although Google says it treats sub domain and root domain same but according to my experience, this is not the case everytime. Because when we go to google and register a root domain "www.example.com" then it is submitted but when we buy or add subdomain "subdomain.example.com" then we have to submit this in Google. If in real, they are the same thing for Google then submitting one (the root domain) should also the cause for subdomian but that is not. Well, it depends on experience. See further screenshots below. My experience is subdomain are somehow treated as a separate entity by Google.
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  Brenda Michelin: There have been a thousand Algo updates since those posts were written.
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  Eva Brown: Yes, but not much change in this matter of domain and sub domain and sub directory. If there would be then John Muller must update about it like he did about the previous one.
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  Eva Brown: Who cares. Yet PBN are used and it is not hidden. Google knows. Backlinks gigs are being sold on Fiverr as a legit seller and Google knows it too. What I told is just my experience, read my first reply. I am not imposing my experience on anyone. What Google changes in its algo is also revealed after some experiments and my experience about subdomain is not yet changed even after June 2019.
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  Michael Martinez: If the subdomains link to the root domain WITHOUT using "rel=`nofollow`" attributes the subdomain links will carry as much value as any other links. The idea that the algorithms automatically assume a subdomain is a "separate site" is not only incorrect, it`s a non sequitur.