I am following English Grammar in Use by Raymond Murphy: unit 114 is about "in case".
The author mentioned the use of 2 tenses(present and past) with "in case":
Do not use will after "in case". Use a present tense for the future.
You can use in case + past to say why somebody did something.
Here are 2 examples of present tense given by the book:
- Your car should have a spare wheel in case you have a puncture.
- I'll remind them about the meeting in case they've forgotten.
And 2 examples of past tense:
- I left my phone switched on in case Jane called.
- We rang the doorbell again in case they hadn't heard it the first time.
I can understand examples about present simple and past simple, but I can't figure out the difference of choosing present simple and present perfect, and of choosing past simple and past perfect.
I know that 'perfect' describes something happened in the past and have/had effect on a certain moment(the current momenta or a moment in the past.) I have problem to distinguish the difference in meaning in this case. What's the difference in meaning between "simple" and "perfect" in this case?