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 ha tabun tosyokan 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 ha tadasii kotae de ha arimasen.
The shop is likely closed.
みせ は おそらく 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 おねえさん は ます。kitto oneesan ha kimasu.
It will surely snow.
きっと ゆき が ります。kitto yuki ga hurimasu.
They will surely be late.
きっと かれら は おくれる。kitto karera ha okureru.
sure, certain; reliable
たしtasika
surely; certainly; indeed
たしか にtasika 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。tasika ni ano mise ha simatte iru.
This is indeed his wallet.
たしか に これ は かれ の さい 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
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 wo mitukemasu.
(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 tanzyoubi wo oboete imasu.

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