The Grammar of Standard English
The grammar of Standard English is much more stable and uniform than its pronunciation or word stock: there is remarkably little dispute about what is grammatical (in compliance with the rules of grammar) and what isn't.
Of course, the small number of controversial points that there are--trouble spots like who versus whom--get all the public discussion in language columns and letters to the editor, so it may seem as if there is much turmoil; but the passions evinced over such problematic points should not obscure the fact that for the vast majority of questions about what's allowed in Standard English, the answers are clear.
(Rodney Huddleston and Geoffrey K. Pullum, A Student's Introduction to English Grammar. Cambridge University Press, 2006)