These two phrases are considered quite advanced but quite useful as well. They are however, quite commonly confused from one another as they are quite similar. We’ll discuss both of them in today’s blog so buckle up and 勉強しましょう!(Benkyou shimashou: Let’s study!)

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For today’s blog, we can give you a few tips on how to express “must”, “have to”, and “need to” in Japanese.. If you have encountered these grammar points before, you probably have an inkling on how similar yet different they are. They are used to signify one’s “obligation”–something you have to do. As they are intermediate grammar points, don’t feel disheartened if you don’t get it straight away. It will take a lot of practice and repetition to get it but it definitely will all pay off in the end. Hopefully, this blog will help you better understand when to use these phrases as they are very useful and can definitely make you sound more fluent!

As mentioned above, the phrases/sentence patterns we will discuss today technically have the same functions or meanings. They all signify needing to do something or having an obligation that you need to do. There is, however, a slight nuance between them which we can hopefully communicate well enough in this blog for you to understand. These nuances are very subtle and are usually only noticed and used by native speakers– more reason for you to try and apply it with your own grammar

〜いけない (Ikenai) and its usages

In “-ikenai”s case, the action that you are obliged to do is something that you are willingly doing– something you want to do and think needs to be done. The actual sentence patterns used with “-ikenai” are quite straight forward and will be easy to get used to as long as you know the basics.

Verb (ない form, minus the い) + くてはいけません or for a more informal sentence, + くてはいけない. This phrase/ sentence means, “must do”. Please take a look at the sample sentences below. 

Isoganakute wa ikenai.
I must hurry.
Mou juu ichi ji da. Nenakute wa ikemasen.
It's already 11 pm. I need to sleep.
Nihongo wo motto benkyou shinakute wa ikemasen.
I must study Japanese more.

Verb (ない form, minus the い) + ければいけません or for a more informal sentence, + ければいけない. This phrase is quite similar to 〜くてはいけません where you must do an action except you think there is no other choice but to do the action you are set to do willingly. This is also used when you are telling someone to do something. Please take a look at the sentence examples below for some references.

Sugu ni ie ni kaeranakereba ikemasen.
You must go home at once
Ashita no asa wa hayaku okinakereba ikemasen yo.
You have to wake up early tomorrow.
Shizuka ni shitei na kereba ikemasen.
You have to keep quiet.

〜ならない (Naranai) and its usages

As mentioned in the introduction to this topic, “-ikemasen/nai” and “narimasen/nai” are very similar in meaning and usage– this phrase also means “must”. One subtle nuance is how this phrase, compared to “-ikenai”, can also imply that this is something the speaker needs to do but doesn’t necessarily want to do. 

Verb (ない form, minus the い) + くてはなません or for a more informal sentence, + くてはならない. Please take a look at the sentences below for some examples.

Now we must talk about important matters.
kore kara daiji na hanashi o shinakute wa naranai.
Kare ni attara oyamaranakute wa naranai yo.
You will have to apologize when you see him.
Watashi tachi wa kankyou wo mamoru you ni doryoku shinakute wa naranai.
We must try to protect the environment.

You can also use the phrase “しなければなりません” (Shinakereba narimasen: I can’t not…) which can be shortened by dropping ければなりません and instead adding 〜きゃ–this makes it very casual and quite playful!

Seiko shitai nara kimi wa motto doryoku shinakereba narimasen.
You must try harder if you want to succeed.
Watashitachi wa jibun no kenkou ni wa jyuubun chuui shinakya.
We must take good care of ourselves.
Sumimasen. Ashita wa shiken da kara, konban benkyou shinakereba narimasen
Sorry. I have to study tonight as I have a test tomorrow.

〜だめ (dame) and its usage

I am sure that you have heard of this word before. It is essentially used by itself meaning “no good” but in this context, it is used as “must” and is considered to be very casual. This is a phrase that should only be used when you are talking to people you are close to and know very well. The sentence pattern for this phrase is Verbて form + は + だめ. Please take a look at the sample sentences below.

Sore wo tabete wa dame.
You must not eat this./Don’t eat this.
Neko chan wo daki agete wa dame yo.
You must not pick up the kitty./ Don’t pick up the kitty.
Hitotsu no koto ni subete wo kakete wa dame da.
Don’t put all your eggs in one basket.
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Like we mentioned in the beginning of this blog, this is an intermediate grammar point so it might take you longer to fully get the hang of using the above phrases for saying “must”. Remember though, いけない(-ikenai) and ならない(-naranai) and usually found at the end of sentences or phrases as that does help in remembering how to use them! Also, だめ(dame) is very casual and shouldn’t be used with someone with a higher social status and in a corporate setting. 

Apply and practice using these three phrases as much as you can– try making 5 sentences/ phrases each for -ikenai, -naranai, and –dame. Just keep on practicing until you get used to using them. If you can practice with a native speaker or maybe even with a friend who is studying Japanese, that would be even better!