Relax: you’re probably not making as many mistakes as you think you are. So says eminent linguist Geoffrey Pullum’s breezy guide to grammar – or, at least, to his own version of it, as previously laid down in mammoth academic treatises.

Literally everything else written about English grammar in the past two centuries, you see, is “hopeless” and a “muddle”. Our re-education requires some renaming of parts of speech and reshuffling of items between them, ensuring a tension between the book’s hope to be a popular guide and the unfamiliarity of its terminology and taxonomy. Pullum even hates the term “parts of speech” itself, insisting that they have nothing to do with speech, which is, at best, an idiosyncratic view and, at worst, an example of how it might be impossible to write about grammar without becoming a little bit crankish.

So bye-bye “conjunctions”; you’ll have to say “coordinators” from now on; meanwhile, “away”, “back”, “here”, “home”, “now” and “there” are reclassified as prepositions rather than adverbs. Pullum gives an argument as to why this interpretation can work, but it is just another interpretation. “How could grammarians blunder so badly?” he moans, without wondering whether the goal of an airtight and objective taxonomy of language, free of ambiguities and exceptions, might be a pipe dream.

Readers are meanwhile reassured that there’s nothing necessarily wrong with the passive, or the split infinitive, or the dangling participle, or adverbs. Pullum is an engaging and friendly writer, always on the side of the ordinary Joe against the nitpickers. A particular delight is how he shows that many “rules” beloved of self-appointed grammar constables were simply made up quite recently by irritable ink-stained wretches. Using “hopefully” as a modal adjunct – eg “Hopefully, the king will knight David Beckham”, not intending to mean that the king will be brimming with optimism while waving his sword – was perfectly fine until a few 1960s New York scriveners decided it was bad.

In general, for Pullum the highest court of correctness is common usage. But he sometimes seems unaware of usages that contradict his claims: “pants”, he writes, is one of a few words “found only in the plural”, which will disappoint devotees of the marvellous fashion singular, gladly teaming a pant with a shoe. And what about the claim that exclamative clauses “always begin with either ‘how’ or ‘what’”? So silly!

If Shakespeare or some other great writer did it, Pullum will usually say it can’t have been wrong. (Therefore he’s intensely relaxed about “between you and I”, when the pedants would have it as “me”.) But when he is writing about the long-used singular “they” (“Nobody here seems to look into an author, ancient or modern, if they can avoid it”: Byron), he insists that the idea “he” can be used in the same way to cover both men and women was invented by an 18th-century female grammarian and “has no basis in the facts of English”. That would have come as a surprise to Thomas Cranmer, who in the Book of Common Prayer (1549) defines a catechism as “an instruction to be learned of every child, before he be brought to be confirmed of the Bishop”, as well as to John Donne, no neglecter of the female sex, when he wrote: “A Christian hath no Solstice … where he may stand still, and go no farther.”

To be sure, I found these citations in the Oxford English Dictionary, and Pullum constantly insists that all modern lexicographers, as well as all grammarians not called Pullum, are wrong about everything, which lends his book a slightly crazed tone of “Who are you gonna believe, me or your lying dictionaries?”. But the record of usage is assuredly one of the facts of English.

The Truth About English Grammar ends with a brief and bland section on style, but the concluding “Further Reading” section is enjoyable for its righteous lampooning of Strunk and White, authors of postwar US handbook The Elements of Style (“flagrant nonsense”) and Orwell’s Politics and the English Language (“dumb advice about writing that no one follows”). For my part, on finishing this book I was seized with the desire to reread Kingsley Amis’s The King’s English, still the only such work that, in its droll suavity, approaches the condition of literature itself.

• The Truth About English Grammar by Geoffrey K Pullum is published by Polity (£20). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply