Making decisions – にする、ことにする、ことになる

Decided to summarize expressing decision making as I already know three ways to do it!

Noun/な-adj + にする

コーヒーにする。
I will have (decide on) coffee.

にしている

This infers that ongoing effort is made, for example like a preference or a habit.

部屋をきれいにしている。
I keep my room clean.

ことにする

Now we can add verb + ことにする, so I can express decisions on actions too and not just a noun.

日本に行くことにした。
(I decided that) I am going to Japan.

ことにしている

Like にしている but can use verbs.

毎朝ジョギングすることにしている。

ことになる

The nuance here is that the decision is not made you. I remember this by like なる is become, so something becomes a decision, doesn’t mean that I made the decision.

日本に行くことになった。
(It has been decided, or some other external factors) I am going to Japan.

ことになっている

Usually used when it’s like a policy, a rule, for example it’s a company policy that every Monday there is a meeting:

会議は毎週月曜日ことになっている。

Could you pretend it did not happen?

Feels like a useful phrase, but I probably don’t know how to make this sentence from scratch, so I might as well write it down 😅

なかったことにしてくれない？

• なかった – did not exist, did not happen
• こと – thing
• にする/にして – A を B にする means to treat A as B, to make A into B
• くれない – くれる means to do for me, くれない is would you not do it for me? which is more like “could you please do it for me”

In this sentence, there is a hidden item, like spilling the juice or an “oopsie” is the thing that we want to treat as なかったこと (the thing that didn’t happen).

The literal translation would be:
Treat it (the oopsie) as something that didn’t happen, could you please do it for me?

The context I heard this in was A and B almost had a one-night stand.

A: 昨日の夜のこと…
B: なかったことにしてくれない？