JLPT N3Mostly writtenConfident

に違ちがいない・に相そう違いないmust be; surely

You are convinced of something you haven't checked: "it must be", "I'm sure". This "must" is never "have to". に相そう違いない says the same in stiff writing.

電でん気きが消きえていて、返へん事じもない。もう寝ねたに違ちがいない。

The lights are off and there is no answer. They must have gone to bed already.

雪ゆきの上うえに大おおきな足あし跡あとがあり、爪つめの跡あともある。熊くまに違ちがいない。

There are large footprints in the snow, and claw marks too. It must be a bear.

How to form it

Plain form + に違ちがいない／に相そう違いない

Past and negative go in the word before it: 寝ねたに違ちがいない, 知しらないに違ちがいない. A noun or a な-adjective drops だ: 熊くまに違ちがいない, 大だい丈じょう夫ぶに違ちがいない (but 熊くまだったに違ちがいない). Polite: に違ちがいありません.

What you go on: Your own reasoning, usually from a clue in front of you: lights off, footprints, a wallet that isn't in your bag.
Tone: Sure of yourself. On a thin clue it sounds dramatic.
Where you'll meet it: Novels, essays, newspaper columns, the reading passages in exams. More written than spoken.

In use

これだけ駅えきに近ちかければ、家や賃ちんは高たかいに違ちがいない。

This close to the station, the rent must be high.

財さい布ふは机つくえにも鞄かばんにもない。家いえに置おいてきたに違ちがいない。

My wallet isn't on the desk or in my bag. I must have left it at home.

この筆ひっ跡せきは以い前ぜんの手て紙がみと同おなじです。書かいたのは同おなじ人じん物ぶつに違ちがいありません。

This handwriting is the same as in the earlier letter. It must have been written by the same person.

How sure?

	How sure, and why
来くるかもしれない	"Might": possible, but you wouldn't bet on it.
来くるでしょう	"Probably": a guess.
来くるはずだ	"Should": you have a schedule, a promise or a fact to go on.
来くるに違ちがいない	"Must be": you are convinced, usually by a clue in front of you.

In conversation

Said to a friend, に違ちがいない sounds like a line from a novel. People say きっと…と思おもう, or, surer still, 絶ぜっ対たい…だよ.

あれだけ練れん習しゅうしたのだから、本ほん番ばんでも大だい丈じょう夫ぶに違ちがいない。

After all that practice, she is sure to be fine on the day too.

Written, or thought to yourself.

あれだけ練れん習しゅうしたんだから、本ほん番ばんでもきっと大だい丈じょう夫ぶだと思おもうよ。

After all that practice, I'm sure she'll be fine on the day too.

To a friend.

あれだけ練れん習しゅうしたんだから、本ほん番ばんでも絶ぜっ対たい大だい丈じょう夫ぶだよ。

After all that practice, she'll definitely be fine on the day too.

To a friend, and surer still.

絶ぜっ対たい, also 絶ぜっ対たいに, is "definitely", and with a negative "never", "no way": 絶ぜっ対たい行いかない.

彼かれは絶ぜっ対たい来くるよ。

He'll definitely come.

間ま違ちがいない: "no doubt about it"

あの声こえは山やま田ださんだ。間ま違ちがいない。

That's Yamada's voice. No doubt about it.

Said every day.

に相そう違いない

The same meaning and the same way of attaching, in stiff writing: legal papers, older novels.

これだけの証しょう言げんが一いっ致ちしている以い上じょう、彼かれは事じ実じつを知しっていたに相そう違いない。

With so much of the testimony in agreement, there can be no doubt that he knew the facts.

Close neighbours

はずだN4

It needs grounds you could name: the schedule says so. に違ちがいない can rest on a hunch.

時じ刻こく表ひょうでは、電でん車しゃは十じゅう時じに着つくはずです。

According to the schedule, the train should arrive at ten.

に決まっているN2

Spoken and insistent: "of course it is", as if nobody could think otherwise.

外そとは雪ゆきなんだから、寒さむいに決きまってるよ。

It's snowing outside, so of course it's cold.

Check yourself

1What does this mean?

彼かれは明日あしたも来くるに違ちがいない。

Choose an answer to see why.

2Which one is right?

Choose an answer to see why.

More sentences

ドアに鍵かぎがかかっている。彼かれはもう出でかけたに違ちがいない。

The door is locked. He must have gone out already.

何なん度ど電でん話わしても出でない。まだこの知しらせを知しらないに違ちがいない。

However many times I call, there is no answer. I'm sure they don't know the news yet.

部屋へやは暗くらく、物もの音おともしない。今いまは誰だれもいないに違ちがいない。

The room is dark and there isn't a sound. There must be no one there now.

メールの署しょ名めいを見みるかぎり、新あたらしい担たん当とう者しゃは森もりさんに違ちがいない。

Going by the email signature, the new person in charge must be Mori.

机つくえの上うえに温あたたかいお茶ちゃがある。誰だれかがさっきまでここにいたに違ちがいない。

There is warm tea on the desk. Someone must have been here until just a moment ago.

Compared with similar forms

Saying how sure you are: "probably", "should be", "must be"