Levels of certainty

QuestionAnswer
probably, perhaps
ぶんtabun
(He)'s probably already sleeping.
ぶん もう て いる。tabun mou nete iru.
The book is probably in the library.
ほん は ぶん しょかん に あります。hon wa tabun toshokan ni arimasu.
probably, perhaps
おそらくosoraku

Same degree of confidence as ぶん, but more formal.

That is likely not the correct answer.
おそらく それ は ただしい こたえ で は ありません。osoraku sore wa tadashii kotae de wa arimasen.
The shop is likely closed.
みせ は おそらく まって います。omise wa osoraku shimatte imasu.
surely, certainly
きっとkitto
(Your) older sister will certainly come.
きっと おねえさん は ます。kitto oneesan wa kimasu.
It will surely snow.
きっと ゆき が ります。kitto yuki ga furimasu.
They will surely be late.
きっと かれら は おくれる。kitto karera wa okureru.
sure, certain; reliable
たしtashika
surely; certainly; indeed
たしか にtashika ni

Where きっと expresses a strong belief or confidence that something will happen or is the case, 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.
たしか に あの みせ は まって いる。tashika ni ano mise wa shimatte iru.
This is indeed his wallet.
たしか に これ は かれ の さい です。tashika ni kore wa kare no saifu desu.
That's certainly the case, isn't it?
たしか に そう です ね。tashika ni sou desu ne.
definitely; necessarily; invariably
かならkanarazu

かなら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.
かならず こたえ を つけます。kanarazu kotae o mitsukemasu.
(He) always remembers the birthday without fail.
かならず たんじょう を おぼえて います。kanarazu tanjoubi o oboete imasu.

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