なくてはいけない

The grammar pattern なくてはいけない expresses obligation or necessity – that something must be done. It translates to "must do," "have to do," or "need to do" in English.

The pattern is formed by taking the negative form of a verb (ない), replacing ない with なくて, and adding はいけない:

• たべる食べる → 食べない → 食べなくてはいけない (must eat)
• いく行く → 行かない → 行かなくてはいけない (must go)
• する → しない → しなくてはいけない (must do)
• くる来る → 来ない (こない) → 来なくてはいけない (must come)

The literal meaning is "if one does not do X, it is no good", which produces the sense of obligation.

Polite form

To make it polite, change いけない to いけません:

Casual contraction: なくちゃ

In casual speech, なくてはいけない is frequently shortened to なくちゃ] (dropping いけない entirely) or なくちゃいけない.

Related patterns

• なければならない – Another common way to express "must do," slightly more formal in tone.
• てはいけない – Expresses prohibition ("must not do"), which is the opposite meaning. Be careful not to confuse the two:
  • 食べなくてはいけない = must eat
  • 食べてはいけない = must not eat