Grammar - Beginner - Part 4
nakereba ikenai なければいけない
Predicative phrase (expressing obligation imposed by the speaker) meaning: (you) must.
Nakereba is the ba-form of the negative adjective nai. It may be replaced with nakutewa, nai to, or the informal nakya.

1. After the stem of nai-form of verb

もっと勉強しなければいけません。
Motto benkyou shinakereba ikemasen.
You must study harder.

「私も行かなければいけませんか。」「いいえ、結構です。」
''Watashi mo ikanakereba ikemasen ka.''Iie, kekkou desu.''
''Do I have to go, too?'' ''No, you don't need to.''

2. After ku-form of adjective

もっと軽くなければいけません。
Motto karuku nakereba ikemasen.
It needs to be lighter.

3. After (adjectival) noun + de

老人に親切でなければいけません。
Roujin ni shinsetsu de nakereba ikemasen.
You must be kind to old people.

-> See also: nakereba naranai, nakutemo yoi
 
nakereba naranai なければならない
Predicative phrase (expressing obligation/necessity of the speaker) meaning: have to.
Nakereba may be replaced with nakutewa or the informal nakya.

1. After the stem of nai-form of verb

九時までに会社に行かなければなりません。
Ku ji made ni kaisha ni ikanakereba narimasen.
I have to go to the company by nine o'clock.

もっと単語を覚えなければなりません。
Motto tango o oboenakereba narimasen.
I have to learn more words.

2. After ku-form of adjective

アパートは駅にもっと近くなければならない。
Apaato wa eki ni motto chikaku nakereba naranai.
The apartment house needs to be much closer to the station.

3. After (adjectival) noun + de

話は論理的でなければならない。
Hanashi wa ronriteki de nakereba naranai.
The speech needs to be logical.

-> See also: nakereba ikenai, nakutemo yoi, neba naranai