Much like てはいけない
states that something ‘must not’ be done. However, this is where the similarities end. なくてはいけない
is an example of a double negative in Japanese, and actually has the meaning ‘(A) must be done’, or ‘must do (A)’.
While this grammar point is usually translated as ‘must do’, the literal translation is ‘must not, not do (A)’. This double ‘not’ is where many learners have difficulties. いけない
simply means ‘cannot go’, and comes from the negative potential form
To use this structure, simply create the negative form of a verb, and then convert ない to なく (the conjunctive form of an い-Adjective
), followed by て
. After this, は
is added, and then finally いけない
Today, I must sleep at 9. (I must not, not do it)
I must buy my girlfriend's birthday present tomorrow. (I must not, not do it)
Since my friend is coming tomorrow, I must clean my house. (I must not, not do it)
is considered to be the most common structure used with the ‘must’, and ‘must not’ grammar points, and is natural in both speech, and written Japanese. Alternatively, ならない
may be used in formal speech, but is much better suited to writing. だめ is also acceptable, but much more casual than either いけない
After breakfast, I must drink my medicine.
You must also eat vegetables.
The ては in なくては is often converted to ちゃ, as this is easier to say. なくちゃ
may then be followed by いけない
, or いけない
may be omitted, without changing the meaning.
I gotta go to the company on Saturdays too.
Today, I gotta go to the supermarket.
These casual structures are very similar to words like ‘gotta’ in English.