場合はif; in case of
場合 means "case". 場合は names a situation that may come up, and the rest of the sentence says what to do or what applies. It is the "if" of notices, manuals and rules.
In case of fire, do not use the elevator.
If you can't attend, please let us know by the day before.
How to form it
Plain form + 場合は
行く場合は, 忘れた場合は, できない場合は, 重い場合は. The word before it usually stays plain, even in a polite sentence.
With a noun or a な-adjective
Noun + の + 場合は ／ な-adjective + な + 場合は
雨の場合は, 必要な場合は. Also 場合には, or just 場合、.
What to do, case by case
A sign, a manual, an app or a letter from school names the case first, then gives the instruction or the rule for it. Staff and teachers talk this way too when they explain a procedure.
If you have forgotten your password, select the password-reset link.
If you are a student, please show your student ID.
If the package is heavy, please have two people carry it.
Two phrases to use yourself
その場合は is "in that case", and 私の場合は is "in my case".
I may not be able to go tomorrow.
In that case, please get in touch by the morning.
In my case, it took three years.
A case, not a time
English "when" can be either. 場合 picks out one case among several; it doesn't say when. The time something really happened is とき.
When the earthquake happened, I was at school.
A time. It happened, and that is when.
In case of an earthquake, get under a desk.
A case. It may happen, and this is what to do.
Why た, when it hasn't happened?
た before 場合 isn't the past. It says the thing will have happened by the time you act.
If you are going to be late, please call.
You call before you are late.
If you arrive late, please give your name at reception.
By then you are late.
Among friends
The everyday "if" is たら. Friends can use 場合は too when they make plans, but on a light invitation it sounds like a notice.
Sounds odd: 暇な
If you are free, come over.
Between friends: 暇だったら、遊びに来てね.
Close neighbours
たらN4
The everyday "if" and "when", for plans, invitations and talk.
If it rains, let's watch a film at home.
Check yourself
1Which one fits?
昨日、
Choose an answer to see why.
2Which one fits?
雨
Choose an answer to see why.
3Which one fits?
明日
Choose an answer to see why.
More detail
場合があります
On notices, 場合があります is "there are cases where". English usually says "may".
On days of bad weather, buses may be late.
ている場合じゃない
In conversation, ている場合じゃない is "this is no time to be…".
This is no time to be playing around.
More sentences
If you are not changing the reservation, there is no need to contact us.
If the screen is completely dark, first check the power cable.
If you need further explanation, please contact the person in charge.
In the unlikely event that the alarm sounds, evacuate the building immediately.
If it rains, the ceremony will be held in the gym.
If you don't know the way, please ask the station staff.