Verb after な-adjective, is it necessary to complete the sentence?

Question

I read somewhere that 形容動詞 are a special subclass of nouns. Contrarily 形容詞, the い adjectives, are actually a lot more similar to verbs. During the time that I have been learning Japanese language (almost a year) I have developed the notion that verb is an essential part of a complete sentence and な-adjective can not fullfill the duty of the verb. Yet, In The essence of sentence construction on Tae Kim's Blog, the part about Treating verb phrases as nouns, in order to make a sentence, な-adjective is used as a substitute for verb and だ comes after that only "If you don’t want to sound girly". In this example on Tae Kim's Blog

たくさん運動するのはいいが、ちゃんと休むのも大切。

is being treated as a complete sentence and then we read:

Finally, let’s add a bit of motherly advice-sounding nuance to it and give it a more conversation style, since it sounds like the speaker is trying to admonish the listener.

たくさん運動するのはいいけど、ちゃんと休むのも大切よ。

If you don’t want to sound girly, you’ll want to add 「だ」 when using 「よ」 with nouns/na-adjectives.

たくさん運動するのはいいけど、ちゃんと休むのも大切だよ。

My question is that, in order to make a complete sentence , 大切 being a な-adjective, why it is not necessary for a verb to come after it?

Answer 1

I may be misunderstanding your question but I don't think a verb is always necessary after なadjective. In this case, you can think of it that there is a be-verb and sometimes the be-verb is hidden.

This sentence is omitting the be-verb and it means "It's good to exercise a lot but taking a break is also important".

たくさん運動するのはいいが、ちゃんと休むのも大切。

The be-verb for this sentence could be

たくさん運動するのはいいが、ちゃんと休むのも大切です。(formal)

or

たくさん運動するのはいいが、ちゃんと休むのも大切だ。(casual)

The よ is just a post positional particle, not a verb. You can look up 終助詞 for more explanation on this. In short, it kind of adds a little more nuances to the sentence.