> 旅行の出発日は八月三十日になった。  
>  部屋は綺麗になった

> 宿題をしなかったので留年することになりました

Can someone explain the difference between になる and ことになる？ as per the above
examples?
CC BY-SA 4.0
2021-12-07T04:46:57.927
91507
2021-12-09T14:09:27.660
2021-12-07T06:37:50.400
30454
47028
question
meaning
になる and ことになる？旅行の出発日は八月三十日になった。
になる means _to become/change of state_ ; ことになる means _it is decided that_ (the
decision being made by someone other than the speaker).

  * [【JLPT N５】文法・例文：〜なる](https://nihongokyoshi-net.com/2019/03/13/jlptn5-grammar-naru/)
  * [【JLPT N4】文法・例文：〜ことになる](https://nihongokyoshi-net.com/2019/05/02/jlptn4-grammar-kotoninaru/)
CC BY-SA 4.0
2021-12-08T07:55:12.777
91524
2021-12-08T11:09:42.733
2021-12-08T11:09:42.733
45489
45489
91507
answer
Of the three sentences you posted only the last one's meaning is
unquestionably clear.

> 旅行の出発日は八月三十日になった。  
>  部屋は綺麗になった  
>  宿題をしなかったので留年することになりました

That's because of missing context.

Let's start with the last one.

The grammar here is

> ...することになりました

This is a fixed form whose mean is that _someone_ decided some action. There
is a related form

> ...することにしました

which means _I_ (or the natural subject of the sentence) decided on some
action.

The first two sentences don't fall into this category. Nothing is being said
explicitly in them about decision made by someone else.

But without context it's hard to say what's going on.

> 旅行の出発日は八月三十日になった。

simply says

> The day for setting out on the trip was set to August 30th.

Why this was the case or who really had a say in the day is not clear without
more context. Note, it could be a situation, let's say, where your boss set
the date for the trip. But as I mentioned above, this is not explicitly
expressed there in the sentence. Context would be necessarily to read it that
way.

Similarly, with

> 部屋は綺麗になった  
>  The room became pretty.

There could be any number of reasons for this. It could be something natural,
like how the morning sunlight lit up the room on a particular day. It could be
incidental, someone put flowers in the room and brightened the mood of the
room. It could just be that someone cleaned the room. But regardless of
context, the room somehow was made beautiful.
CC BY-SA 4.0
2021-12-09T14:09:27.660
91544
2021-12-09T14:09:27.660
4875
91507
answer