Translation guide
Expresses the speaker's strong belief that something is not the case, based on evidence or reasoning. In Japanese, this is typically conveyed through sentence-ending patterns that combine probability with negation.
The speaker is fairly certain that something is not true, often based on some evidence or logical deduction.
Standard pattern for 'probably isn't'. Attaches to nouns and na-adjectives. For i-adjectives and verbs, use the plain negative form + だろう.
彼は学生ではないだろう。
He probably isn't a student.
それは簡単ではないだろう。
That probably isn't easy.
Casual/spoken form of ではないだろう. Very common in everyday conversation.
それ、本当じゃないだろう。
That probably isn't true.
Polite version of ではないだろう. Use in formal settings or when speaking politely.
明日は雨ではないでしょう。
It probably isn't going to rain tomorrow.
Polite but slightly softer than ではないでしょう. Common in polite conversation.
それは問題じゃないでしょう。
That probably isn't a problem.
Literary/formal negative volitional auxiliary meaning 'probably won't' or 'probably isn't'. Attaches to the dictionary form of verbs. Rare in modern speech.
彼はもう来るまい。
He probably isn't coming anymore.
The speaker wants to express a negative opinion or fact less directly, often to be polite or avoid confrontation.
Literally 'I think it might not be...'. Softens the assertion. Very common in both speech and writing.
この計画は成功しないのではないかと思う。
I think this plan probably isn't going to succeed.
Rhetorical negative question form meaning 'isn't it probably the case that...?'. Used to present a conjecture politely.
彼はもう知っているのではないだろうか。
He probably already knows, doesn't he? / I suspect he probably already knows.
While 多分 means 'probably', it is typically used with affirmative statements. To express 'probably isn't', you need the negative form of the verb/adjective plus だろう/でしょう. Simply saying 多分〜ない can sound incomplete or unnatural without the sentence-ending particle.
多分彼は来ないだろう。
He probably isn't coming.
だろう is the plain form, used in casual speech, writing, or when thinking to oneself. でしょう is the polite form, used in formal situations or when speaking to superiors. Both can express probability, but でしょう can also be used to seek agreement (like a tag question).