Meaning & usage
に違いない expresses a very strong conviction that something must be true, used when the speaker infers a conclusion from evidence or reasoning rather than stating a confirmed fact. It attaches to the plain form of verbs and i-adjectives, as in 書いたに違いない or 高い に違いない, and to nouns and na-adjective stems, as in 兄弟に違いない, with だったに違いない for past nominal predicates. It sounds assertive in speech and writing, but it is not used for promises or facts the speaker has confirmed.
Example sentences 7
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私たちは道をまちがえたにちがいない。
We must've taken the wrong road.
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シャロンはやり手にちがいない。
Sharon must be a go-getter.
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そのなかに、何か重いものが入っているにちがいない。
There must be something heavy in it.
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うれしいお知らせにちがいない。
Without a doubt, this is good news.
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外国へ行くのは高くつくにちがいない。
Visiting a foreign country must be expensive.
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弟がこの手紙を書いたにちがいない。
My brother must've written this letter.
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あの人はトムの兄弟にちがいない。
He must be Tom's brother.
In past JLPT papers
This came up in 1 past exam question.
