I am confused about using had, talking about walking into a building in the past tense:
I can't reword this and really don't understand which is right and why. Or maybe:
You don't need to use the past perfect for a second time. Swan in Practical English Usage has a section called tense simplification in subordinate clauses (p573). He states:
If the main verb of a sentence makes it clear what kind of time the speaker is talking about, it is not always necessary for the same time to be indicated again in subordinate clauses. ... Verbs in subordinate clauses are often simpler in form than verbs in main clauses, for example...simple past instead of past perfect.
- I hadn't understand what she said. (More natural than...what she had said.)
So, "She had been humming when she walked into the building" is the better choice here.
Had doesn't seem necessary to convey the fact that the person was humming and walking in to a building.
"She had been humming when she had walked into the building." The easiest way to pass on the information to the reader would be something like this:
"She had been humming when she walked into the building." If you're married to the idea of using 'had' in the sentence, then only 1 'had' would be necessary, since 'walked' already shows that this action was done in the past.
She had been humming when she had walked into the building.She had been humming when she walked into the building.
The past perfect is used in narrative to add background and context to the main event: it describes an action that has finished at the time referred to.
The main event is then described in the simple past.
She had been humming is in the past perfect because it gives context/background to the main event, which is "she walked into the building", which, you will note is in the simple past.
She hummed as she walked into the building.
She was humming as she walked into the building.
These are essentially the same. But the first is the most direct and clear.
She had been humming as she walked into the building.
This distinguishes two time periods in the past, and therefore confuses the action. It implies a prior action (humming) that ended at the start of the second action. It makes sense only if the sentence is, "She had been humming, then walked into the building" or similar.
If the humming continued throughout the entrance, it makes no sense to distinguish two time periods. "Had been" places an action farther in the past. "She had been planning to visit New York, but went to Denver instead to see her cousin."
If there was a need to have a prior time period, the structure might be something like this:
She had been humming as she strolled through the park, and continued humming as she walked into the building.
This is an excellent question! I had been thinking about the same "problem" for quite a while and posted hereon with good but not very satisfactory feedback from the community.
The answer to your question is that your option 2 is correct. The reason is 'sequence of tenses'.
Here, from 'A Practical English Grammar' by A.J. Thompson (1986):
Why Simple Past follows Past Perfect when the former is a subordinate clause is a question that I cannot answer. (Maybe that's simply how English works.) To language learners, from a point of logic, one would use Past Perfect for both, in the main clause and the subordinate clause. However, that is usually not correct.
