When do I have to use 午{ご}前{せん}中{ちゅう} and 朝{あさ}?


I am confused with the usage of 午前中 and あさ. When should they be used properly?

明日のあさに銀行で口座を開きます。

明日の午前中に銀行で口座を開きます。




If you mean "morning", I think they're often interchangeable. The native
Japanese 朝 is more common, and if I search the [_Balanced Corpus of
Contemporary Written Japanese (BCCWJ)_](http://www.kotonoha.gr.jp/shonagon/)
for your particular phrase, we find about a five-to-one ratio in favor of 朝:

[code]

       明日の朝に　　　　　50 results
       明日の午前中に　　　10 results
    
[/code]

In general, I would say there's no difference in meaning. Both typically refer
to "morning", which is most commonly the period of time after the sun rises.
When I look up 朝 in dictionaries, they're ambiguous about when it ends--for
example, 明鏡国語辞典 says it can refer to either a short while after the sun rises,
or it can extend all the way to roughly noon:

> 夜が明けてからしばらくの間。また、夜が明けてから正午ごろまでの間。

Literally speaking, you might expect 午前中 to refer more properly to the twelve
hours from midnight to noon, so that would be a difference in meaning. And in
certain contexts such as [weather
forecasts](http://www.jma.go.jp/jma/kishou/know/yougo_hp/saibun.html), it has
exactly that meaning, while 朝 is more restricted, so they aren't always strict
synonyms. But in many contexts, I think 午前中 refers to roughly the same span of
time as 朝.

Sometimes 朝 might be conceptualized more like a point in time, while 午前中 is
always a span of time thanks to 中. So 朝ずっと is a little unusual, but 朝からずっと
"ever since this morning" is fine; and 午前中ずっと "all morning" is fine, while
午前中からずっと is silly:

[code]

       朝ずっと　　　　　　1 result
       午前中ずっと　　　　11 results
       朝からずっと　　　　28 results
       午前中からずっと　　0 results
    
[/code]

I think Eiríkr Útlendi is correct that the Sino-Japanese 午前中 belongs to a
slightly more formal register, but it's a common phrase and I think you can
use it in casual conversation if you like.

