When or If
Look at the following sentences:
a. We will go home when it stops raining.
b. If it stops raining, we will go home.
What is the difference between the two sentences?
• When is used for things which we are sure to happen.
Example:
I will go jogging this afternoon. (Plan) When I go jogging, I will drop by Susan’s place.
• If is used for things that will possibly happen.
Example:
Don’t call me if I am late this evening. My meeting might get extended.
If the company doesn’t call me, I will send them an email.
I might attend the conference tomorrow. If I attend the conference, I will try to find a chance to show our new proposal.
Going back to the two sentences presented at the beginning, sentence A implies that the rain is sure to stop, thus they will go home (after it stops). Sentence B, on the other hand, implies that the speaker is not sure whether the rain will stop later or not.