～わけがない
there’s no way / impossible
～わけがない attaches to a plain-form clause and expresses the speaker's strong conviction that something cannot possibly be true. The noun わけ means “reason” or “case”, so the pattern literally says “there is no reason for that to be so”. In English it can be translated as “there's no way ...”.
1. Denying a possibility outright
The clause before わけがない can itself be negative. In that case the two negatives combine into an emphatic positive: “there's no way he doesn't know” means “he definitely knows”.
彼が知らないわけがない。
“There's no way he doesn't know.”
- 彼（かれ）= he
- が = subject marker
- 知らない（しらない）= doesn't know
- わけがない = there's no way (that ...)
2. Saying something is out of the question
With a positive clause, ～わけがない flatly rejects the possibility. In casual speech the が is often dropped: ～わけない.
こんな難しい問題、私にできるわけがない。
“There's no way I can solve such a difficult problem.”
- こんな = this kind of
- 難しい（むずかしい）= difficult
- 問題（もんだい）= problem
- 私（わたし）= I
- に = marks who has the ability
- できる = can do
- わけがない = there's no way
How to form it
Plain form + わけがない (na-adjectives take な: ～なわけがない)
- できる = can do → できるわけがない = there's no way (I) can do it
- 言う（いう）= to say → 言うわけがない（いうわけがない）= would never say
- 簡単（かんたん）= easy → 簡単なわけがない（かんたんなわけがない）= there's no way it's easy
Key idea
～わけがない is not a neutral guess, it is the speaker's firm judgment that something is impossible. If you can say “absolutely not, that can't be” in English, ～わけがない fits.
Built on the same stem
Updated .