Translation guide
The English word "doubtful" can express uncertainty about facts, suspicion about people or situations, or low probability. This guide helps learners choose natural Japanese expressions for each nuance.
Expressing that you are not sure whether something is true or will happen.
The most direct equivalent for "doubtful" in the sense of questionable or uncertain. Often used for facts, statements, or outcomes.
その話は少し疑わしい。
That story is a bit doubtful.
彼が時間通りに来るかどうかは疑わしい。
It's doubtful whether he will come on time.
Pattern for "it is doubtful whether..."
彼が本当にそれをやったかどうか疑わしい。
It's doubtful whether he really did it.
Often means "suspicious" but can also mean "doubtful" or "unreliable" for information or weather. More colloquial than 疑わしい.
明日の天気は怪しい。
Tomorrow's weather is doubtful.
その情報はちょっと怪しいね。
That information is a bit doubtful, isn't it?
Literally "it is questionable." Used when you have doubts about the validity or truth of something.
その計画の成功は疑問だ。
The success of that plan is doubtful.
Formal/literary expression meaning "not certain" or "unclear." Used for facts or memories.
その噂の真偽は定かではない。
The truth of that rumor is doubtful.
Expressing that someone or something seems dishonest or not to be trusted.
The go-to word for "suspicious" or "doubtful" in the sense of seeming dishonest or shady. Can describe people, behavior, or situations.
あの人は怪しい。
That person looks doubtful/suspicious.
怪しい取引が行われている。
Doubtful transactions are taking place.
Literally "cannot be trusted." Direct way to say someone or something is doubtful in terms of reliability.
あの情報源は信用できない。
That source is doubtful/untrustworthy.
Expressing that something is not likely to happen or be true.
Common way to say "unlikely" or "doubtful" for events. Literally "doesn't seem like it will happen."
彼が来るのはありそうにない。
It's doubtful that he will come.
雨が降るのはありそうにない。
It's doubtful that it will rain.
Literally "the possibility is low." More formal and objective.
成功する可能性は低い。
The chances of success are doubtful.
Means "prospects are dim" or "unlikely." Often used for hopes or expectations.
彼の回復の見込みは薄い。
His chances of recovery are doubtful.
Expressing personal doubt or lack of conviction about what to do or believe.
Literally "half-believing, half-doubting." Used when you are not fully convinced.
その話を聞いて半信半疑だった。
I was doubtful about that story.
To feel doubtful/questionable about something. Verb phrase.
彼の説明を疑問に思った。
I felt doubtful about his explanation.
Literally "cannot have confidence." Expresses personal doubt.
それが正しいかどうか確信が持てない。
I'm doubtful whether that's correct.
疑わしい is more about factual doubt or questionable truth, while 怪しい leans toward suspicion of dishonesty or shadiness. 怪しい is more common in everyday speech for people and situations.
彼の証言は疑わしい。
His testimony is doubtful (questionable truth).
あの男は怪しい。
That man is suspicious/doubtful.
When describing a person as "doubtful" in the sense of suspicious, 怪しい is much more natural. 疑わしい人 sounds like "a person who is doubted" rather than "a suspicious person."
彼が同意するかどうかは疑わしい。
It's doubtful that he'll agree.
天気が怪しい。
The weather looks doubtful.
彼の話は半信半疑だ。
I'm doubtful about his story.
Stronger than 怪しい, implies something smells fishy or is clearly dubious. Colloquial.
彼の言い訳は胡散臭い。
His excuse is doubtful/suspect.
Can also be used for suspicious character, but slightly more formal and less common in casual speech than 怪しい.
彼の行動は疑わしい。
His behavior is doubtful.