How to tell them apart
ろくに〜ない judges the quality or adequacy of an action — the subject does it, but poorly or insufficiently (ろくに勉強もしない). 滅多に〜ない judges frequency — the event almost never happens at all (滅多に起きない). Swapping them is wrong because a rare event isn't necessarily done poorly, and a poorly-done action isn't necessarily rare.
- ろくにない Use ろくに〜ない when someone does an action but does it poorly, inadequately, or half-heartedly.
- 滅多にない Use 滅多に〜ない when something happens so rarely that it is almost never seen or experienced.
| Grammar point | Meaning | JLPT level |
|---|---|---|
| ろくにない rokuninai | scarcely; insufficiently; to only a small degree; almost not at all | N3 |
| 滅多にない ninai | Infrequently; on rare occasions; almost never | N1 |
ろくにない rokuninai
scarcely; insufficiently; to only a small degree; almost not at all
ろくにない is a negative expression meaning something is hardly done or barely adequate. It attaches to a negative verb, as in ろくに知らない or ろくに食べないで, and emphasizes that the action is far from sufficient. It carries a critical tone, suggesting the amount or ability is disappointingly small.
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この若者は、自分の国についてろくに知らない。
This young man knows little about his country.
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彼女はろくに食べないで席を立った。
She had only eaten a little before she left the table.
滅多にない ninai
Infrequently; on rare occasions; almost never
滅多にない is an adverbial expression meaning something happens very rarely. It is placed before a negative verb, as in 滅多にやらない or 滅多に歌わない, and can combine with ほとんど for emphasis. It always pairs with a negative form, never an affirmative one.
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メアリーは滅多にやらないって、トムが言ってた。
Tom said that Mary seldom does that.
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彼女は滅多に歌わないが、今夜は歌うと思う。
She seldom sings, but I think she will tonight.
ろくにない and 滅多にない are JLPT N3–N1 grammar points that Japanese learners often mix up. This page compares them side by side on meanings, usage and example sentences, so you can tell them apart.