I've been reading Oliver Kamm's Accidence will Happen: The Non-Pedantic Guide to English (2015) - or move over Miss Grundy. Here are some of the passages I have highlighted:
Whatever is in general use in a language is for that reason grammatically correct. (This is a quote from an 1892 English grammar book.)
The reason for speaking and writing in Standard [English] forms isn't to show refinement; it is to make us at home in the world.
Show me a style guide and I'll show you preferences smuggled in and depicted as rules.
Prohibitions on the passive voice, on conjunctions at the beginning of sentences, on prepositions at the end of them and on much else besides have nothing to do with good grammar.