Tenses and parallel construction

Day 28

Tenses and parallel construction:

If a sentence starts with a particular tense, the same tense should be carried forward throughout the sentence.
The above rule holds true for future and present tense.

Exception to the rule:

The use of past perfect : when two events take place in past , the previous event will take a verb in past perfect while the later will take a verb in the simple past.

eg. The train had left the station when we reached the platform.

In this sentence two events have occurred. First event is Train left the station. and second event is we reached the platform. Out of these two events 1st event happened first so it should have verb in past perfect so the second event should have verb in simple past.