Conditional sentences. Main clause: “will”, “if” clause: verb in past

Sentences that use “will” in the main clause and the past tense in the “if” clause refer to an action that is complete. Therefore, these conditional sentences have the following form:

Simple future, If/When + past perfect

For example, consider the following sentence:

We will visit him, if he has moved into his new dorm.

In this sentence, the speaker will visit someone if the move is complete.

Both “if” and “when” can be used for these sentences. A conditional clause using “if’ suggests something happens less frequently. Consider the following sentence:

I will take a bag of marshmallows if I go to the campfire tonight.

Notice the difference in the following sentence:

I will take a bag of marshmallows when I go to our weekly campfire tonight.

Usage of the word “when” in a conditional sentence suggests that something happens regularly.