なければならない

Like なければいけない, なければならない is a structure that implies that something 'must be done'. However, it is important to remember that this is actually a double negative, and therefore means 'If (A) is not done, it cannot become', or more simply '(A) cannot not be done'.

To make this construction, the auxiliary verb ない will need to be conjugated with ば, creating なければ (if not). After this, ならない (to not become) will be added to the end.

As we learned in the なきゃ lesson, なければ may be shortened to なきゃ. This structure is frequently used, either with or without the added ならない.

Caution

While いけない (to not be able to go) and ならない (to not become) are quite similar, ならない will rarely be used outside of formal situations, or in writing. Due to this, いけない will be heard much more frequently in speech (when it is not omitted).