JLPT N3: に違いない (must be; [I'll] bet [you that]...)

When you want to emphasize that you are pretty sure something is true, you can use に違いない (にちがいない).

An example:

岡田さんのお姉さんは宇宙飛行士だそうだ。きっとものすごく頭がいいに違いない。
おかださん　の　おねえさん　は　うちゅうひこうし　だ　そうだ。　きっと　ものすごく　あたまがいい　にちがいない。
Apparently Okada-san’s older sister is an astronaut. She must be extremely smart. [I’ll bet she’s extremely smart.]
Literally: “Okada-san + の + older sister + は + astronaut + だ + そうだ (=[hearsay marker]). + surely + extremely / to a very great extent + smart (=head + が + good) + must be / I'll bet that (=に違いない).”

に違いない is stronger than "probably" but not as strong as "definitely."

If we were to explain it in Japanese, we could say that it means「きっと～と思う」(きっと～とおもう // I'm pretty sure...; I'm almost positive).

Back in the day, I had a Japanese teacher tell me that something that's きっと is 90% likely to be true. The more I get exposed to Japanese, the less I think that's the case. Sometimes it seems a bit lower than 90%. Then again, the dictionary says: きっと (surely; undoubtedly; almost certainly; most likely [e.g. 90 percent]). So maybe I'm the one who's mistaken. Rei agrees with me, though.

Anyway, yeah:

きっとものすごく頭がいいに違いない。
きっと　ものすごく　あたまがいい　にちがいない。
She's extremely smart.
Literally: “surely + extremely / to a very great extent + smart (=head + が + good) + must be / I'll bet that (=に違いない).”

↓　↓　↓

きっとものすごく頭がいいに違いない。
きっと　ものすごく　あたまがいい　にちがいない。
She must be extremely smart. [I’ll bet she’s extremely smart.]
Literally: “surely + extremely / to a very great extent + smart (=head + が + good) + must be / I'll bet that (=に違いない).”

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I've always thought that に違いない was kind of a fun phrase.

違い (ちがい) can mean something like "difference" or "discrepancy."

And the verb 違う (ちがう) can mean "to differ" or "to be wrong."

If we just guess that this ない means "there isn't," then we can imagine that this is saying "there is no discrepancy."

Help... I'm being... pulled... into... tangent land!

🐘🐘 Tangent Land 🐘🐘

When I was a beginner at Japanese, I remember hearing something like this multiple times, with varying degrees of exaggeration:

Japanese people avoid confrontation more than anyone on the planet. They don't even have a word for "wrong." They just say "that's different" when they think something is incorrect.

Socially, I agree that Japanese people avoid direct confrontation. And the Japanese language coincides with this.

But when I hear someone quite forcefully saying 違うよ！ (ちがうよ！), they are not saying "That's different!" They're saying "Wrong!", "No!", etc.

I love Japan, but I think people romanticize it a bit too much from time to time, and this is one such case. It reminds of this lesson, when I talked about how it's a bit ridiculous that people praise Japan's concept of 腹八分目 (はらはちぶんめ // lit. "belly + eight + parts + eye [="-th" in this case]).

Japanese people are human beings. And human beings say things like "That's wrong." This is much like how you might tell me I'm wearing a stupid hat when you say "That hat's... interesting..."

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OK. I'm back.

Where were we?

Oh yeah, grammar. Ugh.

Put pretty much anything in plain form in front of に違いない：

Plain Form Whatever ＋ に違いない
must be [whatever]; (I'll) bet (you that) [whatever]

Varieties of "whatever" we see in this lesson: VERBS, i-adjectives, and NOUNS.

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Your brother's wallet was stolen! You say:

弟の財布を盗んだのは、さっきすれ違った男に違いない。
おとうと　の　さいふ　を　ぬすんだ　のは、　さっき　すれちがった　おとこ　にちがいない。
I'll bet you that man who passed by earlier was the one who stole my (little) brother’s wallet.
Literally: “younger brother + の + wallet + を + stole + のは, + earlier + passed by + man + must be / I'll bet that (=に違いない).”

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Some dude is quite obviously pretending to be asleep. You say:

彼は寝たふりをしているに違いない。まぶたがピクピク動いている。
かれ　は　ねた　ふり　を　している　にちがいない。　まぶた　が　ピクピク　うごいている。
He’s just pretending to be asleep. His eyelids are twitching.
Literally: “he + は + pretending to sleep (=slept + pretending) + を + is doing + must be / I'll bet that (=に違いない). + eyelids + が + twitching (=twitchingly + are moving).”

Is "twitchingly" even a word? I don't think so.

Using words like ピクピク (i.e. onomatopoeia) is a really tricky party of mastering Japanese because they are so common. There are really just too many to count. I'm actually thinking about doing a series of lessons on this in the near-ish future.

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You're almost done:

彼らは、イギリスが島国であることを知らなかったに違いない。
かれら　は、　イギリス　が　しまぐに　である　こと　を　しらなかった　にちがいない。
I'll bet you that they didn’t know the U.K. is on an island.
Literally: “they + は, + U.K. + が + island country + である (=is) + こと + を + didn’t know + must be / I'll bet that (=に違いない).”

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Finished!

If you're still not feeling comfortable with this grammar point, no worries. We're looking at practically the same thing in our next N2 lesson.