This lesson will now look at the "must" phrases. There will be more variation in forms to be aware of in this section, and the grammar complications will be harder than with the "must not" forms, but don't worry.
The first four basic patterns are ～なければならない, ～なければいけない, ～なくてはならない, and ～なくてはいけない. Just as with must not phrases, ～ては contracts to ちゃ in colloquial speech. Other contractions include ～なければ → なけりゃ and ～なくてはいけない shortened to just ～なくちゃ.
|動詞||未然形||食べ＋ない|| → て → 連用形 → 食べなくては ＋ ならない・いけない|
→ ば → 已然形 → 食べなければ ＋ ならない・いけない
|形容詞||連用形||新しく＋ない||→ て → 連用形 → 新しくなくては ＋ ならない・いけない|
|形容動詞・名詞||連用形||新鮮で＋ない||→ ば → 已然形 → 新鮮なければ ＋ ならない・いけない|
Chart Note: Example verbs may not be perfect for demonstrating the actual sensitive nuances of the options to be discussed in this lesson.
|～なければ → ～なきゃ||～なければ → ～なけりゃ||～なくては → ～なくちゃ|
Variant Note: ～なきゃ and ～なくちゃ are often used without anything after them.
～なくてはならない VS ～なければならない
Just as how ～てはならない concerns prohibition （禁止） and is used in the written language not to describe personal matters but societal duties in regards to law and societal norms, ～なければならない is used for affirmative must commands. When the command of duty is directed towards individual responsibility rather than society or some institution as a whole, ～なくてはならない is acceptable.
The nation must directly ensure a bare minimal lifestyle to all citizens.
Employees must record in the time recorder one's leave time.
Interchangeability in the Spoken Language
However, unlike straight-up prohibition, we find all four options ～なければならない・～なければいけない・～なくてはならない・～なくてはいけない acceptable in the spoken language. This is a perfect opportunity to get familiar with casual speech. Take note of contractions. Consult the chart above in case you forget.
The country has to provide a bare minimal lifestyle to all citizens.
I have to go home and take care of my little sister.
I have to return the book.
6. てめーは死ななきゃ。(Masculine; vulgar)
You have to die.
In everyday conversation, these four patterns have great interchangeability. If we are to talk about the extremities of the usages of ～なくてはならない and ～なければならない, the difference would be this.
～なくてはいけない：Duty or command to the addressee (which may be oneself or another party) regarding common sense, morality, societal common wisdom, or current conditions. The speaker is directing the addressee. When used towards oneself, you treat yourself as the 'addressee'. If referring to oneself, a first pronoun is usually needed to tell that you mean this.
～なければならない：A duty of the speaker in regards to common sense, morality, and or societal common wisdom. It will show responsibility burdened upon the speaker. The person bearing the responsibility is not excluding to the speaker, but it is best described as being the subject. This may be be used in the spoken language as well, and this is also when you may see the polite form ～なければなりません.
When you use ～なければ, you imply an obvious duty with no penalty involved for not complying. ～なくては is used when there is a penalty for not complying. いけない is in regards to the listener or one’s conscious and ならない is used in regards to the speaker. So, when we say things interchangeable, we’re saying that if we change one for the other, the new nuance still makes sense. It is not the case that the meaning stays completely the same.
You must hurry.
Children must go to bed early.
We must avoid an excess of waste.
It's because I have to play with my little brother.
You have to drink water every day. (General you, which includes oneself)
I have to catch the boat.
You have buy the new book.
Word Note: ｛その・あの｝新しい本 may be more natural in many contexts than 新刊, which can also be interpreted as "new publication". Nevertheless, 新刊 is still a commonly used word.
～ないといけない & ～ないとだめだ
As you would imagine, the rules governing these phrases is just like when used for must not. ～ないとならない doesn’t exist. And, these two phrases are quite removed semantically from the others. You can’t tell whether the speaker’s duty or addressee’s duty is being referred to without relying on context, so it is typically only used in the spoken language or writing which can reflect back on the conditions in a dialogue. As this phrase particularly blurs the existence of penalty, it has a lightly feeling and is used a lot in the spoken language because of this.
Because the particle と is used, though, your statement should be one based on experience or knowledge of some sort. Though the situation is somewhat more ambiguous than with must not phrases, you can still see how ～ないといけない refers to rule-like behavior and ～ないとだめだ may hint at the existence of a consequence for not following through.
I gotta go home quick and take care of my little sister.
I have to wake up early tomorrow 'cause I have an exam.
It's a matter of life or death, so I/you need to take measures.
18. 明日までに報告書を書かないとだめだよ。(Casual yet serious)
I/You have to write a report by tomorrow!
Casual Speech Note: In colloquial speech, you can simply use ～ないと.
I've got to go.
There are many other older and dialectical variations of what we have just learned. As for old phrases, we have ～ねば｛ならない・ならぬ｝，and ～なければならぬ which are old-fashioned but not so archaic that they don’t frequently show up in the written language. You may also see the very stiff ～なるまい. ～ねばならない in particular is extremely common in literature.
I felt that from now on that we would have decide on our own accord concerning ourselves. That is
because we must live on just the three of us.
21. 何としても合格せんばならんねな。(Old-fashioned; dialectical)
You have to pass no matter what.
From 蒼氓 by 石川達三.
Base Note: The old みぜんけい of する, せ-, must be used with ～ぬ.
Variant Note: There are several important notes about the above sentence. The ～ね in せねば is contracted to ～ん and ～ない in ならない becomes → ～んね, which would be realized today in Modern Japanese as the casual ～んねー such as in 分かんねー・分かんない.
Important Dialectical Variants
Sometimes "must" is expressed completely differently in other dialects. The most common dialect pattern is "未然形 ＋なあかんで". You can also see ～ねば contracted to ～にゃ in Western Japanese Dialects.
いけない is very sensitive in respect to dialect. Below is a chart of the most common variations you may encounter.
I have to sing.
1. せにゃならん ＝ しなければならない
2. せないかん ＝ しなければならない
3. Note 2 is also a Western Japanese dialect example. Here, we see a rare example of ～ない following the old 未然形 of the verb する, せ-, and あかん contracted as かん.