いわんや

adverb

much more; let alone; not to mention

Formal, somewhat literary adverb used to emphasize that if something is true for a lesser case, it is even more true for a greater case. Often follows a negative statement or a rhetorical question, and is typically paired with ～さえ or ～すら. In modern Japanese, ましてや is more common in everyday speech.

• 大人おとなでさえ難むずかしい。いわんや子こ供どもには無む理りだ。

  It's difficult even for adults, let alone children.

• 彼かれは簡かん単たんな計けい算さんもできない。いわんや複ふく雑ざつな方ほう程てい式しきなど解とけるはずがない。

  He can't even do simple calculations, much less solve complex equations.