たことにする / たことになる

たことにする / たことになる means pretend to; see things as untrue; contrary to the truth ~. It is a JLPT N1 Japanese grammar pattern used to express that you are deliberately treating something as true (even though it isn’t) or that a situation forces you to accept a version of events that isn’t real.

This grammar point appears often in formal arguments, storytelling, official statements, and JLPT N1 reading sections. If you want to express deliberate rewriting of facts or the unavoidable logical conclusion that something must be considered to have happened, たことにする / たことになる is the pair you need — because it separates conscious pretense from passive, forced acceptance.

What does たことにする / たことになる mean?

Use たことにする when you deliberately treat a past event as true, even though it didn’t happen — to pretend, to proceed as if something occurred, or to consciously ignore the real facts.

Use たことになる when external logic or evidence forces you to accept that something did occur, whether you like it or not — the conclusion that something “ends up being the case” contrary to the truth.

Natural translations include:

• pretend to; decide to act as if ~
• it would mean that ~; it ends up that ~; it follows that ~ (contrary to reality)

The best translation depends on the sentence. Is the speaker choosing the fiction, or is the fiction being imposed by circumstances? That tells you which pattern fits.

How to form たことにする / たことになる

Attach ことにする or ことになる directly to the plain past (た) form of a verb.

Verb (た-form) + ことにする

Verb (た-form) + ことになる

Examples of the pattern:

• 行っ(いっ)たことにする
• 聞か(きか)なかったことにする
• 参加(さんか)したことになる
• 全員(ぜんいん)が賛成(さんせい)したことになる

The form before the grammar point matters. In JLPT questions, wrong answer choices often show ことにする / ことになる attached to the wrong tense or to a noun without の — because the structure only works with a verb in the た-form. When you need to use a noun, you must nominalise it first (e.g. その話(はなし)はなかったことにする).

When is たことにする / たことになる used?

Use たことにする / たことになる in situations like:

• deliberately ignoring an unpleasant fact and proceeding as if it never happened (たことにする)
• describing a forced conclusion that, based on the evidence, a certain event must be regarded as having occurred (たことになる)
• creating a shared fiction in a story, plan, or social situation
• highlighting the gap between reality and an accepted narrative

Tone and register:

• formal to neutral; common in written arguments, business logic, and narrative reasoning
• in casual speech, たことにする appears often, while たことになる leans more logical/reported
• Common in test questions, essays, official statements, and JLPT N1 reading

たことにする / たことになる example sentences

After reading each sentence, ask what job たことにする or たことになる is doing: is the speaker actively choosing to treat something as true (たことにする), or is an external chain of reasoning forcing that conclusion (たことになる)? That makes the nuance easier to remember than a one-word translation.

Nuance of たことにする / たことになる

The core distinction is agency: たことにする is a conscious decision to pretend, while たことになる is an objective (or imposed) consequence that leads to the same result — a fact stated as reality even though it isn’t.

This matters because learners often translate both as “pretend” or “end up that.” But a pattern that looks simple can signal who is in control of the narrative: you, or the logic of the situation.

In many N1 reading questions, the distinction between these two determines the right answer. If the context talks about a personal decision, たことにする; if it describes an inevitable logical outcome, たことになる.

たことにする / たことになる vs ふりをする

Both たことにする and ふりをする can express pretending, but they work differently.

たことにする:

• focuses on the status of an event — treat it as having happened or not
• often used in narrative, logic, and decisions, not for visible acting

ふりをする:

• focuses on external behaviour — act as if a condition is true right now
• usually involves visible fakery: sleeping, knowing, not noticing

Quick contrast examples:

• 見(み)なかったことにする (I’ll treat it as if I didn’t see it — I choose to ignore it)
• 見(み)なかったふりをする (I’ll act as if I didn’t see it — I physically pretend not to have noticed)

If both translations seem possible, check the tone: ふりをする points to a performance you put on, while たことにする points to a mental or narrative decision. In formal reasoning, you almost always need たことにする/たことになる, not ふり.

Common mistakes with たことにする / たことになる

Watch out for these mistakes:

• Using たことになる when you mean a deliberate choice, or たことにする when logic forces a conclusion — the agency flips the meaning.
• Forgetting the た-form before こと; learners sometimes attach the dictionary form (することにする is a different grammar: “decide to do”).
• Treating the pattern as interchangeable with ふりをする without considering the abstract vs. physical nature of the fakery.

A helpful practice method: write a sentence where you deliberately pretend something didn’t happen (たことにする), then rewrite it with たことになる to see how the meaning shifts from “I decided” to “it follows that…”.

Is たことにする / たことになる on the JLPT?

Yes. たことにする / たことになる is commonly taught as JLPT N1 grammar.

That means learners should be able to:

• recognise both patterns in reading
• understand the direction of agency and consequence
• distinguish them in multiple-choice questions where the difference decides the answer

For test preparation, study the grammar point in full sentences. JLPT N1 questions often test whether you understand who is controlling the narrative — the subject (たいことにする) or the situation (たことになる).

Practice questions for たことにする / たことになる

Try making your own sentences with these prompts:

• Use たことにする to describe a situation where you choose to forget something painful and act as if it never happened.
• Use たことになる to describe a conclusion where, based on a set of facts, a certain event must be considered true even though it feels wrong.
• Write a pair of sentences: one with たことにする, one with ふりをする, and explain why you can’t swap them.
• Take a sentence from section 4 and rewrite it swapping たことにする for たことになる; describe how the speaker’s position changes.

Keep your first sentences simple. Once the structure feels natural, add more context so the nuance becomes clear.

Learning path for たことにする / たことになる

To learn たことにする / たことになる efficiently, start with their formation, then compare the two forms head-to-head, and finally practise with real scenarios.

1. First, make sure you can form たことにする and たことになる without looking at the pattern chart. Drill the た-form attachment until it’s automatic.
2. Next, compare たことにする with たことになる in the same sentence frame. Decide which one matches “I decided” and which one matches “the facts force it.”
3. Finally, write sentences where たことにする / たことになる is necessary; then check whether replacing it with one of the related patterns below changes the meaning.

Related grammar to review next

• たはずみに / たひょうしに — because it also deals with events that happen contrary to intention, often triggering an unreal sequence
• たところで — because it also involves assumptions about a result that may not match reality
• たつもりはない — because it also talks about personal stance versus what actually happened
• すら / ですら — because it can appear in arguments where unexpected extremes force a conclusion (たことになる)

Learn たことにする / たことになる with Hane

If you want to review たことにする / たことになる together with the related patterns above, Hane helps you practice Japanese in short, focused sessions.

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