That’s what I’d go with, yeah. We talk about “adjectives” as a distinct class in English, which makes sense, because English adjectives don’t really act like anything else. But the ancient Greek and Roman grammarians thought of adjectives and pronouns as two special types of nouns: in those languages, you can use an adjective anywhere you’d use a noun (compare “the good, the bad, and the ugly”, or simply “the news”: the stuff that’s new). In Japanese, I would say there are two separate classes of adjectives: “noun-like adjectives” and “verb-like adjectives”, and one is closed while the other is open. The fact that we call them both “adjectives” is just a translation artifact.
What do I mean by “closed” versus “open”? (I feel like I said this further up the thread, but a search isn’t finding it…I love having memory problems.)
In each language, it’s really easy to add new words of certain types, and really hard to add words of other types. In English, nouns and verbs are open: we all accepted “Google” and “to Google something” very quickly. But pronouns are closed: singular “they” has been in the language for centuries, and people are still arguing over whether it’s valid or not! Compare how easily English-speakers as a whole accept a new name versus a neo-pronoun.
Which categories are open and closed varies by language, though. In Japanese, pronouns are open, but verbs are closed. When they borrowed “party” from English, they only borrowed it as a noun: you can’t “party” in Japanese, you have to “host a party”, or “go to a party”, or “join a party”, using an existing verb. Verb-like adjectives are also closed in Japanese, while noun-like adjectives are open.[1]
Swahili has a distinct class of adjectives like English does, separate from its verbs and its nouns, but that class is quite firmly closed. New adjectives get borrowed as nouns instead, attached to the sentence with “of”. The only color adjectives in Swahili are “black”, “white”, and “red”; if you want to say something is green, you say it is “of leaves”, gray is “of ashes”, brown is “of coffee”. They borrowed “blue” and “pink” from English, but only as nouns: things aren’t blue, they’re “of blue”.
Prepositions in English used to be entirely open, which is why we have such an enormous variety of them, especially starting with a- and be-. Most languages don’t have a single-word preposition for “athwart”! Even in fairly recent times, most languages wouldn’t be as accepting of new prepositions like “contra”, “circa”, “re”, “apropos”, and “vis-à-vis” as English is. Pronouns and conjunctions are our truly closed classes, and even then, I’ve heard computer science undergrads say “xor” without hesitation…
There are a handful of exceptions, of course; “open” and “closed” aren’t absolutes. You can Google something in Japanese, because “Google” happens to look very much like a Japanese verb. ↩︎