たことにする / たことになる | Grammar

Structure

[verb た] + ことにする [verb なかった] + ことにする

[verb た] + ことになる [verb なかった] + ことになる

Note: Most common with past affirmative (た) or past negative (なかった) forms to pretend something did or did not happen.

Description

The structures たことにする and たことになる are used when something is treated as if it happened (or didn't happen) contrary to the actual truth. They express the idea of pretending, deciding to regard something as true/untrue, or a situation being officially treated in a way that differs from reality.

たことにする – Deliberately pretending

たことにする means to deliberately decide to treat something as if it happened (or didn't happen), even though reality is different. The subject actively chooses to pretend or act as though something is the case.

。

I'll pretend I didn't hear that.

。

Please pretend you didn't know about this.

This pattern is used with the negative past form (なかったことにする) to express "pretend something didn't happen":

。

Let's pretend we didn't see it.

It can also be used with the positive past form to pretend something did happen:

、。

Let's just say we've already read it and move on.

たことになる – Resulting situation / being treated as

たことになる describes a situation where something ends up being regarded a certain way, often by others or by circumstance, regardless of the actual truth. The nuance is that the pretense or interpretation is not necessarily the speaker's active choice – it is how things turn out or how they are officially regarded.

、。

If you stay silent, it'll be taken as if you admitted it.

じょう上。

On paper, it's treated as though I resigned.

Key difference

ことにする → active decision to pretend (the speaker or someone else deliberately chooses to treat it that way)
ことになる → resulting interpretation (it ends up being regarded that way, often beyond one's control)

This parallels the broader distinction between ことにする (decide to) and ことになる (it has been decided / it turns out that).

Common patterns

なかったことにする – pretend it didn't happen
なかったことになる – it ends up as if it didn't happen
～たことにしてくれ / してください – asking someone to pretend something is the case

Examples

。

Please pretend you didn't hear what I just said.

。

Let's pretend that incident never happened.

、きごう？

Let's just say we've already eaten and skip ordering dessert, shall we?

。

She pretended she didn't see anything.

。

Pretend I was never here.

、。

If he doesn't say anything, it will be taken as if he agreed.

、。

According to the contract, it's treated as though I left the company at the end of last month.

、。

If you stay quiet like this, it'll end up looking like you lied.

、。

My attendance was treated as if it didn't happen, and I didn't get the credits.

だっ。

Let's just say it was all a dream.

、。

If you don't submit the report, it'll be as if you didn't do any work.

、。

I knew about it, but I pretended I didn't.