The most standard way of saying “to have to” in Japanese is to say, “if you don’t do (x) then things can’t go well” or “if you don’t do (x) things won’t become”. And we actually have three ways of constructing this logic, each of which follows a double negative pattern to create the expression of “must do”.

【Verb: Neg. conditional ~ば】【いけない or ならない】

【Verb: Negative】といけない

【Verb: nakute te form】は【いけない or ならない】

I have to tidy up.
I have to tidy up.
I need to phone my girlfriend.
Sorry! Today’s impossible. I’ve got a task I need to do.

Note the effeminate omission of the auxiliary verb and のよ at the end.

This morning I had to go to the bank.

This can seem like a tongue-twister at first. In casual conversation there are a couple of ways to abbreviate the phrase. Firstly, the conditional form なければ can be shortened to なくちゃ or なきゃ.

I have a presentation so I need to prepare.
Tomorrow I have a conference call from 8 oclock so I’m got to get to sleep.

Alternatively, you can use a more simple word like だめ in place of “to go” or “to become”.

The exam is right around the corner so you’ve got to study.

Or simply drop the final verb altogether.

I have to do it.
They’re your friend so you need to tell them the truth.
Employees must take a health check-up before joining the company.

One other way to express requirement is to modify the adverbial noun 必要ひつよう.

Foreign students need to register at the ward office.

To form the negative expression we take the te form structure and turn the first clause into the affirmative.

【Affirmative te form】は【いけない or ならない】

Typically いけない is used..

During the exam you are not permitted to use a mobile phone.

The kanji 中 means “middle” and can often be added to other words to mean “during”.

Speaking on the phone is prohibited inside the train.
That is something must absolutely not forget.
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