Levels of certainty

QuestionAnswer
probably, perhaps
多た分ぶんtabun
(He)'s probably already sleeping.
多た分ぶん もう 寝ねて いる。tabun mou nete iru.
The book is probably in the library.
本ほん は 多た分ぶん 図と書しょ館かん に あります。hon ha tabun tosyokan ni arimasu.
probably, perhaps
おそらくosoraku

Same degree of confidence as 多た分ぶん, but more formal.

That is likely not the correct answer.
おそらく それ は 正ただしい 答こたえ で は ありません。osoraku sore ha tadasii kotae de ha arimasen.
The shop is likely closed.
お店みせ は おそらく 閉しまって います。omise ha osoraku simatte imasu.
surely, certainly
きっとkitto
(Your) older sister will certainly come.
きっと お姉ねえさん は 来きます。kitto oneesan ha kimasu.
It will surely snow.
きっと 雪ゆき が 降ふります。kitto yuki ga hurimasu.
They will surely be late.
きっと 彼かれら は 遅おくれる。kitto karera ha okureru.
sure, certain; reliable
確たしかtasika
surely; certainly; indeed
確たしか にtasika ni

Where きっと expresses a strong belief or confidence that something will happen or is the case, 確たしか に often additionally implies that the speaker has evidence or reasoning to support the certainty, or has personally verified the fact.

That shop is certainly closed.
確たしか に あの 店みせ は 閉しまって いる。tasika ni ano mise ha simatte iru.
This is indeed his wallet.
確たしか に これ は 彼かれ の 財さい布ふ です。tasika ni kore ha kare no saihu desu.
That's certainly the case, isn't it?
たしか に そう です ね。tasika ni sou desu ne.
definitely; necessarily; invariably
必かならずkanarazu

必かならずexpresses a strong commitment or assurance that something will happen or is the case. It's often used to make promises or to express unwavering certainty.

(You) will definitely find the answer.
必かならず 答こたえ を 見みつけます。kanarazu kotae wo mitukemasu.
(He) always remembers the birthday without fail.
必かならず 誕たん生じょう日び を 覚おぼえて います。kanarazu tanzyoubi wo oboete imasu.

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