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.
A common na-adjective meaning 'certain' or 'sure'. Often used when you are fairly confident but not 100% sure. Can also be used as an adverb ().
Are you certain he's coming?
We need certain proof.
Means 'to be convinced' or 'to firmly believe'. Stronger than 確か, implying deep conviction.
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.
That person is certainly the culprit.
You'll certainly succeed.
Adverb meaning 'without fail', 'certainly'. Used for future events or obligations. Implies a strong guarantee.
Please come tomorrow without fail.
Adverb meaning 'surely', 'certainly'. Often used when making a confident guess or expressing hope. Softer than 必ず.
I'm sure it'll be fine.
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.
One day, I met a certain bear in the forest.
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.
Means 'fixed', 'constant', or 'a certain (amount)'. Used for quantities, standards, or levels.
Means 'some kind of' or 'certain'. Used when the exact nature is unknown or unspecified. Often in formal contexts.
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'.
He is certain (reliable).
I'm sure he will come.
He will definitely come (no doubt).
When you mean 'a certain person' (unnamed), use ある人, not 確かな人. 確かな人 means 'a reliable person'.
You need to meet certain conditions.
You must meet a certain standard.
For some reason (a certain reason) he didn't come.