Selected answers from the Dumb SEO Questions G+ community.
Martino Mosna: This is certainly true if the links <b>are actually artificial</b>... (of course this could happen even if the unnatural links are 39, numbers don't really matter...)
Matt Raynes: Depends on how the links are built. ; If ethical outreach methods are used you could generate far more than 40 a month and it could be construed as completely natural. ; Exact match anchor text on similar subnets will prick the search engines ears up.
Neil Modi: Yes it is but if you get such backlinks naturally than it will not considered as ;spam. I would suggest to built natural links ;
Bhupendra Rathore: Did you mean i can build more than 40 Back-links if this are natural links/Quality links??
Martino Mosna: "build" and "natural" don't go together very well but yes: if you succeed at gaining more than 40 natural links / month you're doing good indeed...
Dave Elliott: if its 40 blog comments and forum links and rubbish web directories then yeah,(although i've never heard of a number or % being definitive), if they are genuinely useful links from genuinely useful sites then you can add as many as you want.
Neil Modi: ;exactly !!! just keep in mind links should be natural ,should not based repetitive keywords also backlinks are required from quality places.
Subhash Chandra: ;agree with you...if you build links from authority sites and in a natural way, then it is good.
Amahl Majack: I would agree with that assessment. More than 40 links/month would certainly be hard to gain naturally unless a piece of content went viral. Plus, as says, backlinks need to come from quality sources. If you're building 40/month, I'd take a second look at the sites. And from my experience, Page Rank isn't necessarily a reliable measure of quality anymore.