We have been told (in TKD, I think? Was it reinforced later, or taken away?) that klingons only use three classes of words: *) nouns *) verbs *) everything else (the "leftovers") Is this still correct?
Klingon grammarians classify Klingon words into only those three categories, yes. Federation grammarians divide the chuvmey up into subcategories to assist understanding. Both ways are just systems of organizing our understanding of the language and are not prescriptive.
I'm asking because an "adverb" is something I'd like to put in with "verbs", but that is because of the name. Would klingons see an adverb as a form of verb, or as <<chuvmey>> that simply "looks and acts" as a verb, but doesn't follow all the rules. Because if an adverb is considered a verb, shouldn't all verb-affixes be allowed? But if it's a <<chuvmey>>, then it would make more sense to say that as a rule they don't have any affixes, but for this or that word it is known that it may take this or that suffix. They'd simply be special cases, as any language has. (Also, it would keep things simple, IMO.)
An adverb is not a verb; it is a leftover.
Wikipedia defines an adverb as "a word that modifies a verb, adjective, another adverb, determiner, noun phrase, clause, or sentence." It defines an adverbial as "a word (an adverb) or a group of words (an adverbial phrase or an adverbial clause) that modifies or tells us something about the sentence or the verb." Adverbs are a subset of adverbials; the latter has a broader meaning. The Klingon Dictionary uses the word adverbial throughout, not adverb, with two exceptions: naDev, pa', and Dat are nouns in Klingon but adverbs in English; and Klingon adverbials are called adverbs in section 6.7 of the Addendum.
When Federation grammarians group some of the chuvmey into adverbials, they're saying that these are the words that modify the meaning of the verb or sentence, or can sometimes be used as standalone exclamations. There is an exceptional adverbial, neH merely, only that modifies both verbs and nouns, and does so in a unique position (after); TKD admits calling it an adverbial is awkward. The rest of the adverbials modify the sentence by going before the object-verb-subject or law'/puS structure.
Klingon grammarians obviously recognize the adverbial function;
they simply don't give it a name. Some of the chuvmey,
they say, act this way. TKD speculates that Klingon
grammarians lump all the chuvmey together for expediency.
Unfortunately, both Klingonska and <<boQwI'>> only say "adverb" :-(
Labeling them as adverbials would have been better.
-- SuStel http://trimboli.name