Using な after い-adjectives


What does it mean to put a な after an い-adjective? For example, many Youtube
videos are called begin "いいなCM", and a Japanese text book I have uses this
sentence as an example:

> この通りを行くと **大きな** 交差点がある。
>
> Go along this street, and you will find a large crossroads.

What is the meaning of this な? It is also unusual that the 大きい is missing the
final い but the いいな is not. I cannot find it in my textbook or on using
Google.




  * Your example `いいな CM` is not an adjective modifying a noun. It can be taken as a quoted sentence modifying a noun. It may be more recognizable if it were in quotes like `"いいな" CM`. The `な` in `いいな` is a sentence final particle that adds the first person's subjective feeling to the proposition.

  * There are both the i-adjective `大きい` and the (possibly) na-adjective `大きな`. However, whereas the i-adjective has full paradigm, the 大き part in the na-adjective form cannot be extracted and be used like 大きだ. It looks like the na-adjective form is a fossilized form. For this reason, traditional grammar reserves an independent category called 連体詞. The two words are usually interchangable, but for a subtle difference, see the answer here: [i-adjectives used as na-adjectives: is there a difference? (e.g. 大きい versus 大きな)](https://japanese.stackexchange.com/questions/1853).




  * Your example `いいな CM` is not an adjective modifying a noun. It can be taken as a quoted sentence modifying a noun. It may be more recognizable if it were in quotes like `"いいな" CM`. The `な` in `いいな` is a sentence final particle that adds the first person's subjective feeling to the proposition.

  * There are both the i-adjective `大きい` and the (possibly) na-adjective `大きな`. However, whereas the i-adjective has full paradigm, the 大き part in the na-adjective form cannot be extracted and be used like 大きだ. It looks like the na-adjective form is a fossilized form. For this reason, traditional grammar reserves an independent category called 連体詞. The two words are usually interchangable, but for a subtle difference, see the answer here: [i-adjectives used as na-adjectives: is there a difference? (e.g. 大きい versus 大きな)](https://japanese.stackexchange.com/questions/1853).

