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This article is part of the ongoing series “Japanese: the trickier bits”, which delves deeper into some of the more confusing parts of the language. Read the whole series

Primer

If you are studying with the JLPT framework, you will come across ‘must do’ and ‘must not do’ at N4 level. If you’re like me you’ll want to spend a while really wrapping your head around this interesting grammar point.

いけません ikemasen is a conjugation of the verb 行く iku ‘to go’, however it’s usually used to mean ‘is not good’. The grammar points for ‘must do’ and ‘must not do’ both use いけません.

Here are the conjugation rules:

must do = Verb + ない(nai) form + てはいけません

Simply conjugate your verb to 〜ない form then finish with てはいけません.

must not do = Verb + て(Te) form + はいけません

Simply conjugate your verb to 〜て form then finish with はいけません.

…confusing these could potentially cause some problems should you mix them up, which is natural unless you really solidify いけません as negative in your mind…

The confusion

Let’s start with ‘must not do’:

写真を撮ってはいけません (しゃしんをとってはいけません)
You must not take photographs

Unpacking this sentence we see that the verb 取る ‘to take’ has been conjugated to て form and then is followed by いけません ‘is not good’, and the topic is 写真 ‘photographs’.

Honestly, this makes perfect sense so long as you understand いけません to mean ‘is not good’:

“Taking photographs is not good”

Now onto ‘must do’:

写真を撮らなくてはいけません (しゃしんをとらなくてはいけません)
You must take photographs

This is almost the same as ‘must not do’ except we negate the verb 取る ‘to take’, then say いけません ‘is not good’. This means what we’re actually saying is:

“Not taking photographs is not good”

Yep. Double negative, meaning taking photographs is a must!

Take away

You should take some time to process these grammar points as they are confusing and could potentially cause some problems should you mix them up, which is natural unless you really solidify いけません as negative in your mind.

皆さん、happy practising 😀