Translation guide
The English word "certain" has two main uses: expressing sureness or conviction, and referring to a specific but unnamed person or thing. Japanese uses different words and structures for each.
Expressing that you are sure about something, or that something is definitely true.
Referring to a particular person, thing, or amount without naming it exactly.
Pre-noun adjectival meaning 'a certain'. Used before a noun to indicate a specific but unnamed thing, person, or place. Very common in narratives.
確か is an adjective describing a state of being sure. きっと is an adverb expressing a strong belief or hope, often subjective. 必ず is an adverb implying an objective certainty or obligation, like 'without fail'.
When you mean 'a certain person' (unnamed), use ある人, not 確かな人. 確かな人 means 'a reliable person'.
Are you certain he's coming?
確かな証拠が必要だ。
We need certain proof.
Means 'to be convinced' or 'to firmly believe'. Stronger than 確か, implying deep conviction.
私は彼の無実を確信している。
I am certain of his innocence.
Literally 'there is no mistake'. A very common phrase meaning 'certainly', 'without a doubt'. Often used in casual speech.
あの人が犯人に間違いない。
That person is certainly the culprit.
間違いなく成功するよ。
You'll certainly succeed.
Adverb meaning 'without fail', 'certainly'. Used for future events or obligations. Implies a strong guarantee.
明日必ず来てください。
Please come tomorrow without fail.
Adverb meaning 'surely', 'certainly'. Often used when making a confident guess or expressing hope. Softer than 必ず.
きっと大丈夫だよ。
I'm sure it'll be fine.
ある日、森の中でクマに会った。
One day, I met a certain bear in the forest.
ある程度のリスクは覚悟している。
I'm prepared for a certain amount of risk.
Means 'specific' or 'particular'. More formal than ある. Used when emphasizing that it is not just any, but a particular one.
特定の条件を満たす必要がある。
You need to meet certain conditions.
Means 'fixed', 'constant', or 'a certain (amount)'. Used for quantities, standards, or levels.
一定の基準をクリアしなければならない。
You must meet a certain standard.
Means 'some kind of' or 'certain'. Used when the exact nature is unknown or unspecified. Often in formal contexts.
何らかの理由で彼は来なかった。
For some reason (a certain reason) he didn't come.