When you set yourself up as a grammar expert it's better than being an expert on plastics. To be an expert on plastics you actually have to know something about plastics. With grammar the analogous thing doesn't hold. Nobody asks, nobody checks, nobody knows enough to get suspicious. You are free as a bird to publish any garbage you might want to type out.
I discovered this myself while in my favourite used bookstore a few days ago. I was in the language section as usual, and I found The Wordsworth Dictionary of Modern English Grammar by Ned Halley. Says the back cover, "Is there a right way to speak and write English? This unique new guide to the language is dedicated to answering the question - in Plain English. Compiled for readers from school age onwards, this is a book of easy reference."
Well it turns out this book contains a few errors. Here are some:
active and passive In grammar a verb is in the 'active voice' when it describes an action by the subject of the phrase; as, "he gave her the flowers." When the verb describes an action affecting the object of the phrase, it is in the passive voice; as, "she received the flowers from him."
Both these sentences are active. The passive voice is formed by a form of be plus the past participle, for instance The flowers were given to her.
ablative In grammar, the 'case' of a noun or pronoun expressed in the context of location, direction, time or other influences. In the sentence "She sat next to him", the pronoun "him" is in the ablative case. As a determinant of word forms, ablative is not a distinct case in English. In Latin, where nouns, pronouns and adjectives are 'declined' into cases, ablative is the final case in the sequence nominative, vocative, accusative, genitive, dative, ablative.
If English has no ablative, how can him be ablative?
combat Once a mere noun, combat is now in common use as a verb...
The noun and verb are attested at about the same time.
imperfect tense In grammar the tense of a verb describing the progress of an action in the past. In "he was laughing" the verb 'was' is the imperfect tense of 'be'.
was is the past tense. The past imperfect is was laughing.
mood In grammar, the way a verb is used can always be identified with a 'mood.' There are five distinct ones:
1. Indicative mood expressing a fact: 'He is going'
2. Optative mood expressing a wish: 'Let's go'
3. Imperative mood expressing a command: 'Go!'
4. Interrogative mood expressing a question: 'Is he going?'
5. Subjunctive mood expressing a condition: 'Were he to go…'
Optative mood is at least a mood used by some languages (not English). But interrogative mood? It is to weep.
But that's nowhere near the worst of it. The book covers "the curiosities of current slang" as well. Here is the beginning of the entry for Goth:
Goth A worldwide youth 'counterculture' launched, according to some popular historians, by British pop singer Ziggy Stardust - known for his black clothing and eyeliner, white face and piercings - in 1979.
A black-clad, pierced Ziggy Stardust (scientific name: David Bowie) in its natural environment
[It seems that some languages really have an interrogative mood, including Koasati, Yupik and Cubeo.]