The [accepted answer under this
question](https://japanese.stackexchange.com/a/45069/30454) suggests 色々な便利な道具
is natural but it is most likely due to 色々 being an exception. I have just
heard 大きな深刻な問題 on a Japanese TV program. And Google seems to show more
examples with this phrase:

>
> 山梨県の長崎知事は19日、新型コロナウイルスの検査体制の拡充などを発表する記者会見の中で、東京オリンピック・パラリンピックの開催について「国民や県民の健康に極めて
> **大きな深刻な影響**
> を及ぼすような感染状況であれば、オリンピックをやっているどころではない」と発言しました。([source](https://www3.nhk.or.jp/news/html/20210419/k10012984441000.html))

> いま、まさに、これが **大きな深刻な問題**
> になっています。([source](https://www.asahi.com/eco/sympo2010/presen/panel_discussion_8.html))

> まあ、1歳児のこのようなちょっとした問題はいいとして、思春期になってくると、もっともっと **大きな深刻な問題**
> もたくさん起こすのではないでしょうか。([source](https://news.allabout.co.jp/articles/d/87447/))

If I'm not mistaken in 学校文法, 大きな is a 連体修飾詞, and 深刻 a 形容動詞. Is that the reason
why they can be connected with な?
CC BY-SA 4.0
2022-08-24T02:11:57.220
95967
2022-08-24T18:38:28.003
2022-08-24T18:38:28.003
5229
30454
question
grammar particles na-adjectives 連体形
大きな深刻な問題 two na-connected attributives
> If I'm not mistaken in 学校文法, 大きな is a 連体修飾詞, and 深刻 a 形容動詞. Is that the
> reason why they can be connected with な?

I think this is one of the contributing factors. Two 形容動詞 in the same context
would be much more commonly connected with で or かつ, as in 冷静かつ迅速な対応, instead
of 冷静な迅速な対応.

But more generally, the sequence of two attributives (including verbs) does
not make the sentence ungrammatical automatically. It can be understood as a
coordination of two, although it might happen mostly in speech. If it is a
spoken sentence, you might transcribe it as

> これが、大きな、深刻な問題になっています。

It could be an attempt to correct what you have just said. (I think this is
what 学校文法 would discourage, since sentences that include correction can be
seen as broken in that approach.) It could also be intentionally done to have
an emphasis on the second part, somewhat similar to "I did X, or rather [more
accurately said], Y".
CC BY-SA 4.0
2022-08-24T08:24:01.277
95968
2022-08-24T08:24:01.277
10531
95967
answer
大きな is not an i-adjective nor a na-adjective but a fixed _rentaishi_ that
never conjugates. It doesn't have a te-form to begin with, so 大きな深刻な問題 is the
only option if you use 大きな (大きな modifies the noun phrase 深刻な問題 as a whole).
You cannot say 大きで深刻な問題 just as you can't say 色んで便利な道具.

大きい深刻な問題 is not incorrect, but 大きな is [much more common than
大きい](https://japanese.stackexchange.com/a/6694/5010) when used attributively.
If you want to emphasize something has two properties at the same time, using
くて or で may be more explicit on that, so something like 大きくて深刻な問題 might be
better. かつ is even more explicit.

With that said, I also feel 大きな深刻な or 大きくて深刻な sounds fairly redundant... What
is a serious problem that isn't big?
CC BY-SA 4.0
2022-08-24T09:12:57.983
95969
2022-08-24T09:12:57.983
5010
95967
answer