GRAMMAR DETAIL

ないといけない

have to; must

Follows the negative form of a verb to express necessity by presenting the failure to act as an unacceptable situation.

Examples

この薬は毎日食後に飲まないといけない。

I have to take this medicine after meals every day.

出発の一時間前には駅に着かないといけない。

I have to arrive at the station one hour before departure.

明日までに申込書を出さないといけません。

I have to submit the application form by tomorrow.

Structure: A verb's ない form takes といけない, expressing necessity by treating failure to act as unacceptable.
Basic usage: 明日までに申込書を出さないといけません。 means that the application must be submitted by tomorrow.

Necessity expressed through negation
- 出さないといけない rejects the situation of not submitting and thereby expresses a need to submit. It differs from 出してはいけない, which prohibits submission.
Omission in conversation
- The final いけない can be omitted when expressing necessity, as in もう行かないと. In 行かないと会えない, however, the following result makes a conditional sentence, so distinguish the full context.