ずにはおかない / ないではおかない

ずにはおかない means "cannot fail to": something – a film, a speech, an event – is bound to have an effect on people. Take the ない-form and replace ない with ずにはおかない; する becomes せずにはおかない.

The subject is the thing that causes the effect, and the verb is usually a causative of feeling – かんどう感動させる, なかせる泣かせる, おこらせる怒らせる – or a verb like あたえる与える or かえる変える.

ないではおかない goes on the ない-form as it is and means the same; the ず form is the more written. Both are literary – essays, reviews, news commentary. In speech you would say きっと〜～だろう or かならず必ずから～する.

Someone's firm intention

With a person as the subject and a deliberate action, the pattern says that person won't rest until it is done. It sounds determined, sometimes threatening.

ずにはおかない or ずにはいられない

ずにはいられない is about the person who feels the urge: they are the subject, and the verb is plain – I can't help crying. With ずにはおかない, the cause is the subject, and the feeling it produces in others is a causative.

• × 彼の話を聞くと、笑わずにはおかない → 彼の話を聞くと、笑わずにはいられない