The Wrong Thing at the Wrong Moment
ている場合じゃない says an activity is inappropriate given the urgency of the situation.
- 笑っている場合じゃない。(This is no time to be laughing.)
The activity itself is not wrong. The timing is.
It Needs ている
The verb must be in progress, because the pattern criticises something you are doing right now:
| ○ 寝ている場合じゃない | you're asleep and shouldn't be |
| × 寝る場合じゃない | not the pattern |
Against てはいけない
| Pattern | Basis |
|---|---|
| てはいけない | a rule forbids it |
| ている場合じゃない | circumstances make it inappropriate now |
Nothing forbids laughing. The situation simply does not allow for it.
Register
場合じゃない is casual; 場合ではない is the full form. It is most often said to oneself or to a close colleague under pressure, and it carries real urgency.