modality N2 common casualpolitewritten

ものではない — one should not ~

ものではない

Builds on もの

Meaning

one shouldn't ~ / it's not done to ~ — states that an action goes against common sense or social decency

人ひとの悪口わるぐちを言いうものではない。

You shouldn't speak ill of others.

Attaches to	Form	Example
Verb (dictionary form) + ものではない	V(る) + ものではない	笑わらうものではない / 急いそぐものではない

食たべ物ものを粗末そまつにするものではない。

You shouldn't be wasteful with food.

そんなに簡単かんたんに諦あきらめるものではないよ。

You shouldn't give up that easily.

This is the social-norm 'shouldn't' use of もの — the negative twin of the ものだ that states 'that's how one should act'. It carries a faintly preachy, elder-to-younger tone.

Jengo shows ものではない the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.

Sources Compiled with reference to A Dictionary of Advanced Japanese Grammar.