I'm addressing this question because reference to grammar should be trustworthy to non-native speakers like I am. Since we weren't born as native speakers we can't say which grammar rules are obviously true and which are not. From this question: Does the past perfect tense make sense in this sentence? "Sent from an "is" to a "was" before he'd had his breakfast." I noticed that user Nicholas Castagnola disagrees with grammar referenced by other users referencing other sources that say otherwise. To me, a non-native speaker, this appears to be a bit of a problem since I've always trusted Michael Swan's Practical English Usage. However, he, as a native speaker, insists that Michael Swan is wrong here. What do you think of this guys? What grammar books and grammar sites can non-native speakers trust that are referenced by native speakers? I can't be trusting every native speaker's point of view and their reference whereupon I may be mispointed to wrong grammar or worse.
Only the Pope is infallible, but even he has admitted his predecessors have made grave misjudgments and mistakes in the past.
I would still "trust" Swan but that doesn't mean you shouldn't verify his explanations, and remember, he wrote the Bible of grammar, pardon PEU, almost 40 years ago.... the English language has since evolved.
In other words, the book is a very useful and almost indispensable guide, but it is not the "Bible".
What grammar books and grammar sites can non-native speakers trust that are referenced by native speakers?
I don't think that most of the questions native-speakers have about English are about grammar. They are more likely to be about style or usage. Probably the most influential style/usage guides are:
- Merriam–Webster's Dictionary of English Usage (American)
- Garner's Modern American Usage
- Fowler's Modern English Usage (British)
The questions on this site are predominantly from non-native speakers and predominantly about grammar. They need a different set of resources. In my opinion the best and most trustworthy pedagogic or prescriptive grammar resource for ELLs is indeed Swan's Practical English Usage (which would be better called Practical English Grammar).
Probably the two most influential descriptive grammars, which may be consulted by advanced ELLs and native speakers alike are:
- A Comprehensive Grammar of the English Language (1985)
- The Cambridge Grammar of the English Language (2002)
But even these weighty tomes (a total of over 3600 pages) do not cover all the implicit knowledge of grammar acquired by native-speaker adults in their lifetime.
It is no wonder that native speakers growing up with different backgrounds in different countries may have slightly varying 'grammars'. This is the reason for disputes such as the one you refer to in your question. Sites such as this would be less interesting if there were always a single, definitive correct answer.
This is a really good discussion to have. The Stack Exchange solution to this is to have the community vote on answers, and the scores should help non-experts decide whether a claim is credible or not. It is for this very reason that comments are moderated with a heavy hand. Comments can't be down-voted, they can't be updated to clarify points or incorporate community feedback, and they don't have the space to include proper citations to support the claims. They don't even stay in order once people start up-voting them, so it's difficult to follow extended discussions. (Chat rooms on the other hand do keep messages in order, and allow you to see exactly which message a reply belongs to, so they're much better suited for discussion)
As with anything on the Internet, the burden of determining whether something is credible rests with the reader. Visitors should take the information as a whole. What is the score of the answer? If you have the reputation, click on the score and see how many up/down votes it has to get an idea of how controversial it is. Are the cited references both relevant to the point they are said to support and is the information from well-established sites/authors? Do other sources agree with the source being cited ? When you read the information, does it agree with what you already know? Are any points made in comments by the ELL community adequately addressed?
It is difficult for anyone, not just non-native speakers, to know which perspective is correct when a topic is very controversial. When it comes to English, there are many topics where both sides of the argument are perfectly reasonable and the experts disagree with one another. Most of the time on ELL where we deal with the more pragmatic aspects of English, the community very clearly agrees or disagrees with a point of view and I would take any view that is being held by only one person with a grain of salt.
One of the examples given on the question you link to,
"He had been killed before he had breakfast."
implies that the man was killed, then had breakfast. To phrase it like that, you would need to say
"He had been killed before he could have his breakfast."
or (to be fastidious, or possibly even a little pedantic)
"He had been killed before he was able to break his fast."
Seriously, "... before he [X]" strongly implies that he went on to [X] after whatever happened before. And dead people don't generally eat breakfast. Lead, perhaps ...
... in any case, I realise I hadn't answered your question.
Although I don't own a copy I would suggest anything from the Cambridge University press if you're interested in English (UK), and this book if you can obtain a copy is probably a bit dated but was once one of the best guides to avoiding mistakes around. I was amused when searching for it to come across another very similarly titled book which would probably be worth a look.
Finally I will second the recommendation for Fowler's book(s) ... the one mentioned in the other answer isn't the one I remember, but he seemed to know what he was talking about.
It will also be amusing if you find they disagree with me - it's a long time since I read Use and Abuse... :o)