Jisho.org Forum

First of all, with the first question, I'm quite sure you can phrase it like that (I'm a student myself). Your example of あたらしかったです doesn't really help you understand this because it doesn't have an actual noun to modify. There is one but it's assumed. And actually, unless you're describing the noun, you're supposed to put the adjective before the noun.

For your second question, たくさん is a Na-adjective. But it's not like most Na-adjectives because it's also an adverb by itself. What I mean is that with most Na-adjectives, in order to make it an adverb, you に after it. たくさん is both by itself and doesn't require conjugation.

新しかった本 I think is a slightly odd phrasing but is possible in certain contexts, particularly if you qualify it with a time period.

新刊書は一日あたり200点出版されるそうだから、 新しい本が少し前に新しかった本を追い出すのだろう。
(talking about bookstore space) Since around 200 new titles are published every day, new books(1) drive out books that were new(2) only a little before.
(comparing 1 = 新しい本 and 2 = 少し前に新しかった本 )

30年前に新しかった事は30年後には決まった事になっている。
Things that were new 30 years ago become standard thirty years later.

古いメディアが新しかった時
(book title) When ("the time when") old media was new. (here 新しかった doesn't directly modify 時 e.g. it's not "time that was new", it's all of 古いメディアが新しかった that we're using as a modifier).

In your example, as your verb is past tense, the tense of the adjective is talking about the state of the book at the time the action you're describing took place.

新しい本を持ってきた I (or somebody) brought a new book. (the book was new at the time of the action)
新しかった本を持ってきた I (or somebody) brought a book that had been new (but wasn't new at the time the action took place).

Thanks, both of you, this is very helpful.

Kiriain, so was I on the right track in thinking that, in the case of "日本国 には 人々 が たくさん います", takusan is being used as an adverb because imasu is used rather than desu? My theory was that adjectives can't be placed before imasu since the verb means "exist" rather than merely "is". Is this indeed the case?

Yes, TE_Form, that is the case. Because たくさん is used as an adverb, it is placed before います. And what you say is true, います is the verb to exist for animate objects, but it does translate to "is", and "are". Think of how you could say the sentence in English.

"There are lots of people in Japan."
"There is a lot of people in Japan."
"Many people exist in Japan."

Now think of it, which one kinda sounds awkward? I think the third one does.
Also, there is another way you could phrase your sentence.
日本にはたくさんの人がいます。

And of course, this also applies to あります, the "exist" verb for inanimate objects.

Also, I don't think the grammar of your sentence is weird, I think the words used are.
日本国 means Japan. But so does 日本. I think using 日本国 is a bit formal.
Also, 人々 does mean people. But it means "the people". People as a whole. If you're talking about the plural of people, you could just use 人. There is no difference between singular and plural forms in Japanese.