What it means
わけがない expresses a strong belief that something is impossible or cannot be true. It is used when the speaker has a clear reason, evidence, or common sense supporting the judgment. With verbs and i-adjectives, it follows the plain form; with nouns and na-adjectives, it follows な. The polite counterpart is わけがありません, while the preceding word or clause usually remains in plain form.
Usage note
わけがない is stronger than simply saying something is unlikely. Do not confuse it with わけではない, which means that something is not necessarily the case or is not exactly what was stated.
How to use it
これは偶然なわけがありません。
This cannot possibly be a coincidence.
彼の説明が複雑なわけがありません。
His explanation cannot possibly be complicated.
この薬が苦いわけがありません。
This medicine cannot possibly be bitter.
彼がそんな約束を忘れるわけがありません。
He cannot possibly forget such a promise.
これは偶然なわけがない。
This cannot possibly be a coincidence.
彼の説明が複雑なわけがない。
His explanation cannot possibly be complicated.
この薬が苦いわけがない。
This medicine cannot possibly be bitter.
彼がそんな約束を忘れるわけがない。
He cannot possibly forget such a promise.
Example sentences
この古い橋が大雨の後も安全なわけがない。
There is no way this old bridge is still safe after the heavy rain.
彼が三日でこの長い小説を読み終えるわけがない。
There is no way he can finish reading this long novel in three days.
あの小さな店が毎日百人分の弁当