ぬ・
知らぬ is 知らない: ぬ is the old ない. ざる is the same word in a more solemn shape, before a noun: 招かれざる客, an uninvited guest. Both live on in set phrases, proverbs and stiff writing: forms to recognize, not to say.
ぬ
An unexpected power outage interrupted the work.
ざる
This is a fact that is not yet known to the world.
ぬ
Verb ない-form: ない → ぬ する → せぬ
To read it, put ない back: 思わぬ is 思わない. する gives せぬ, so 予期せぬ is 予期しない. It goes before a noun or ends a sentence.
ざる
Verb ない-form: ない → ざる する → せざる
知られざる is 知られない. It goes before a noun, and into ざるを得ない.
Phrases that keep ぬ
These are said and written every day, each learned whole. The last two are formal.
知らぬ間にbefore you know it
Before I knew it, it had got dark outside.
思わぬunexpected
The experiment had an unexpected result.
見知らぬunfamiliar; a stranger
A stranger asked me the way.
何食わぬ顔as if nothing had happened
He continued the meeting as if nothing had happened.
見て見ぬふりturning a blind eye
I can't just look the other way when someone is in trouble.
やむを得ぬunavoidable
Owing to unavoidable circumstances, we are closed today.
More often やむを得ない.
変わらぬunchanging; as ever
We ask for your continued support in the future.
A closing line in business letters.
Proverbs keep it too.
Ignorance is bliss.
Better safe than sorry.
Word for word, a stick before you fall.
ざる before a noun
ざる is the voice of titles, documentaries and solemn writing: 知られざる, "little-known", is a favorite. One phrase everyone knows keeps it.
招かれざる客an uninvited guest
An uninvited guest turned up at the party.
ん is the same word
In speech ぬ wore down to ん: the ん of ません, and of 知らん and 分からん, everyday speech in western Japan and blunt talk elsewhere.
I don't know anything about that.
For reading, not for saying
Outside the set phrases, ぬ belongs to narrators in novels, to samurai and old men in dramas, and to stiff writing. In your own sentences it sounds like play-acting.
No one can know now what was really meant.
A narrator.
One should not rush to a conclusion without sufficient consideration.
Stiff writing. Plainly, しないまま.
Sounds odd: 私は
I do not eat meat.
A samurai's line. You say 食べない.
The same negative in forms still in use
ずにN3
The same old negative in mid-sentence: "without doing". A little stiffer than ないで, and said as well as written.
She left the room without saying anything.
ざるを得ないN2
Circumstances force it, against your wishes: "have no choice but to". Written, and careful speech.
For family reasons, I had no choice but to leave the company I had worked at for many years.
"Unavoidable", as a judgment or before a noun. やむを得ず goes in front of what was done: "having no choice".
The last train had already left, so I had no choice but to take a taxi home.
ねばならないN2
The written "must": なければならない in formal dress.
Now more than ever, we must rethink the system from the ground up.
ねば is ぬ in its ば-form.
The old "must not", with the same ず and ざる: べからず ends a notice or a maxim, べからざる goes before a noun.
This is an outrage that cannot be tolerated in a democratic society.
Check yourself
1You are telling a friend you aren't going tomorrow. Which do you say?
Choose an answer to see why.
2What does this mean?
それは
Choose an answer to see why.
More detail
A ぬ that isn't "not"
In the title 風立ちぬ, "The wind has risen", ぬ is a different old ending, for something that has happened. It sits on the ます-stem; "does not rise" would be 立たぬ.
More sentences
The envoy who was due to arrive had still not come by nightfall.
来ぬ: read こ, as in 来ない.