Noun+Adjective - What are the rules/usages?


I usually self-study, however I see a tutor once a week who is a native from
Tokyo. In my previous lesson with her, she used the following:

> もう夜遅いから家に帰ったほうがいいでしょう。

Where `夜遅い` translates to "late at night", and the overall translation is
something like "Since it's already late, we should head back home."

When I asked her if there are rules governing this construct, she was not able
to give me a definitive answer, but instead was only able to give me one
further example:

> 朝早い = Early in the morning

I am wondering, are these two examples just set expressions, or are there
rules that govern what **`noun+adj`** combinations are possible? Is it
strictly used with **`[unit of time (Noun)]+[qualitative (Adj)]`** , or is
there a wider range of usage?




There actually **is** a rule governing the "Noun + Adjective" structures.

The noun must signify either a **spatial or temporal** unit such as
[朝]{あさ}、[夜]{よる}、[空]{そら}、[天]{てん}、[奥]{おく}、 [時]{とき}、 [数]{かず}, etc.

The adjective must signify a **degree or quantity** regarding the preceding
noun. These include
[早]{はや}い、[遅]{おそ}い、[高]{たか}い、[低]{ひく}い、[多]{おお}い、[少]{すく}ない、[深]{ふか}い, etc.

Thus, it is completely natural and correct to combine these nouns and
adjectives in the "noun + adjective" order without using particles.

Lastly, since adjectives do conjugate in Japanese, these expressions are also
often used as adverbial expressions modifying verb phrases.

Examples of **_adjectival_** usages: 夜遅い、朝早い、空高し、数多い、時遅し, etc.

Examples of **_adverbial_** usages: 夜遅く、奥深く、数少なく、天高く、朝早く, etc.




There actually **is** a rule governing the "Noun + Adjective" structures.

The noun must signify either a **spatial or temporal** unit such as
[朝]{あさ}、[夜]{よる}、[空]{そら}、[天]{てん}、[奥]{おく}、 [時]{とき}、 [数]{かず}, etc.

The adjective must signify a **degree or quantity** regarding the preceding
noun. These include
[早]{はや}い、[遅]{おそ}い、[高]{たか}い、[低]{ひく}い、[多]{おお}い、[少]{すく}ない、[深]{ふか}い, etc.

Thus, it is completely natural and correct to combine these nouns and
adjectives in the "noun + adjective" order without using particles.

Lastly, since adjectives do conjugate in Japanese, these expressions are also
often used as adverbial expressions modifying verb phrases.

Examples of **_adjectival_** usages: 夜遅い、朝早い、空高し、数多い、時遅し, etc.

Examples of **_adverbial_** usages: 夜遅く、奥深く、数少なく、天高く、朝早く, etc.

