に決まっている — Definitely, For Sure

Meaning & Usage

The grammar pattern に決きまっている (ni kimatte iru) expresses a strong conviction, absolute certainty, or a firm conclusion. It conveys the speaker's unwavering belief that something "must be," "is definitely," or "is for sure" the case. This conviction often stems from logical inference, clear evidence, or common sense.

Think of に決きまっている as stating, "There's no way it isn't true," or "It's obviously the case." It captures a feeling of unshakeable certainty. This expression is significantly stronger than simply stating a probability with patterns like ～だろうだろう (darou - probably) or ～かもしれませんかもしれません (kamoshiremasen - might be). It implies that the speaker has thoroughly evaluated the circumstances and arrived at a definitive, unchallengeable conclusion.

This pattern is commonly encountered in spoken Japanese and informal writing. While it conveys powerful conviction, it is generally considered less formal and more direct than ～に違ちがいない (ni chigainai), which also translates to "must be" or "no doubt." に決きまっている often carries a nuance of "it's obvious to anyone" or "it's a given." It can sometimes sound a bit assertive, or even slightly opinionated, especially if used in contexts where the listener might not share the same level of certainty. Therefore, it's important to be mindful of the context and your relationship with the person you are speaking to.

English equivalents for に決きまっている typically include: "It must be...", "It's definitely...", "It's for sure...", "There's no doubt that...", "It's bound to be...", or even "It's a given that...". The underlying idea is that something is so utterly certain that "it is decided" or "it is fixed" to be true. The 決きまっている part literally means "is decided" or "is fixed."

When combined with にに (which indicates the state or result), it forms a powerful declaration of certainty. This isn't merely an assumption, but a conclusion drawn from strong evidence or irrefutable logic, presented as an absolute truth by the speaker. For example, if you see a well-known athlete lining up for a race, you might confidently say, 「彼かれが勝かつに決きまっている。」 (He's definitely going to win.) This expresses your strong belief, based on their past performance or current condition, treating the outcome as a foregone conclusion.

Structure & Formation

The grammar pattern に決きまっている connects to various word types, primarily in their plain forms. For なな-adjectives and Nouns, while their plain forms inherently end in だだ (e.g., 元気げんきだ, 学生がくせいだ), this だだ is almost always omitted when connecting to に決きまっている. This omission is common in natural speech and informal writing, leading to a more direct connection.

It's important to remember that に決きまっている is an intransitive verb phrase. It naturally stays in its ～ているている form, indicating a continuous state of being decided or fixed. Therefore, it's rarely seen in a simple ～るる form like に決きまる.

Example Sentences

General Certainty / Logical Conclusion

Obvious Truth / Common Sense

Strong Opinion / Prediction

Negative Certainty

Common Mistakes

Mistake 1: Over-formal usage or inappropriate assertiveness

❌ 社長しゃちょう、このプロジェクトは成功せいこうするに決きまっています。

✅ 社長しゃちょう、このプロジェクトは成功せいこうすると確信かくしんしております。

Explanation: に決きまっている carries a strong, somewhat assertive tone and is generally more appropriate for informal contexts. Using it with a superior (like your boss, 社長しゃちょう) can sound impolite or overly confident. It might imply that your conclusion is an undeniable fact that even they must acknowledge. For formal situations, expressions like ～と確信かくしんしております (to kakushin shite orimasu - I am confident that...), ～と存ぞんじます (to zonjimasu - I believe/think that...), or ～に違ちがいない (ni chigainai) are more suitable as they convey certainty without the potential for sounding overbearing.

Mistake 2: Using for personal desires or wishes

❌ 宝たからくじが当あたるに決きまっている！ (強つよい願望がんぼう)

✅ 宝たからくじが当あたってほしい！ / 宝たからくじが当あたるはずだ。

Explanation: に決きまっている expresses a conclusion based on evidence, logic, or common sense. It's not used to convey a strong personal wish or desire for something to happen. While you might want to win the lottery, there's no logical basis to conclude it's definitely going to happen. For wishes, use ～てほしいてほしい or expressions of probability if there's some basis. If you strongly expect something to happen based on circumstances, ～はずだはずだ might be more fitting for an expectation rather than an absolute certainty.

Mistake 3: Confusing with simple probability

❌ 明日あしたは晴はれるに決きまっている。（天気予報てんきよほうを見みていない）

✅ 明日あしたは晴はれるだろう。 / 明日あしたは晴はれるはずだ。

Explanation: Unless there's overwhelmingly strong evidence (e.g., you've checked multiple, highly reliable weather forecasts that all agree), stating the weather will "definitely" be sunny with に決きまっている is usually too strong. Weather is inherently probabilistic. Use ～だろうだろう for general probability, or ～はずだはずだ if you have a reasonable expectation. Remember that に決きまっている implies an almost scientific certainty or an obvious conclusion, not just a high chance.

Mistake 4: Incorrect conjugation for Nouns/Na-adjectives

❌ 彼女かのじょは学生がくせいだに決きまっている。

✅ 彼女かのじょは学生がくせいに決きまっている。

Explanation: As noted in the structure section, when connecting to Nouns or なな-adjectives, the copula だだ is almost always dropped for a more natural flow, especially in spoken Japanese. While だだ + に決きまっている isn't strictly ungrammatical, it sounds stilted and less natural than omitting だだ.

Cultural Notes

に決きまっている, while expressing strong conviction, is a very direct and somewhat assertive expression. In Japanese culture, where indirectness and harmony are often valued, using such a strong phrase should be done with awareness of the context and your relationship with the listener. It's perfectly natural among close friends, family, or when expressing an opinion about something widely acknowledged.

However, when speaking to superiors, elders, or in formal business settings, it's generally advisable to soften your certainty. Consider phrases like ～と思おもわれます (to omowaremasu - it is thought that...) or ～でしょうでしょう (deshou - probably, politely). Using に決きまっている in these situations might be perceived as lacking humility or being overly confident, potentially even rude, as it leaves little room for other opinions. It's often used when the speaker feels that the conclusion is so obvious that disagreeing would be illogical.

You'll frequently hear に決きまっている in casual debates, friendly arguments, or when someone is confidently predicting an outcome. For instance, in sports discussions, a passionate fan might exclaim, 「今日きょうの試合しあいは絶対ぜったいに勝かつに決きまっている！」 (We'll definitely win today's game!). This showcases the definitive and conviction-filled nature of the phrase. It's a statement of personal belief that the speaker wants to convey with maximum impact.

JLPT Tips

When encountering に決きまっている on the JLPT N2 exam, pay close attention to the context. The test will often try to distinguish it from similar grammar points that express probability or expectation, such as ～はずだはずだ or ～に違ちがいない. Remember that に決きまっている implies the highest level of personal conviction and perceived inevitability based on evident facts or strong logical inference.

Look for clues in the surrounding sentences that indicate a lack of doubt on the speaker's part. Phrases like 「～からから、絶対ぜったいに～」 (kara, zettai ni - because... definitely...) or 「～はずがないはずがない」 (hazu ga nai - there's no way...) often hint at the strong certainty that に決きまっている conveys. The pattern itself means "it's decided," making the outcome a certainty.

Practice identifying the correct connections for different word types. While verbs and いい-adjectives connect in their plain forms, remember the common omission of だだ for なな-adjective stems and Nouns. Misjudging the formality or the exact degree of certainty can lead to incorrect answers. If a sentence implies a strong, almost undeniable conclusion, especially in a conversational tone, に決きまっている is a very strong candidate.