Page 857 - Wordsmith A Guide to College Writing

using the past perfect tense. Often, writers omit this needed shift and
stay in the simple past tense, thus taking the risk of confusing the

reader.

Examples of Necessary Tense Shifts

past past
By the time Jill woke up, her husband made coffee.

Made coffee should be further in the past than woke up. Had needs to

be used to push made to a time before that indicated by the simple
past tense verb woke.

The minister said a prayer at the grave of Florence Jones, who

attended his church.

Without had, the two verbs in the sentence are, as far as the reader

can tell, occupying the same space in the past. Look at the corrected

versions of the sentences:

past past perfect
By the time Jill woke up, her husband had made the coffee.

past past
perfect

The minister said a prayer at the grave of Florence Jones, who
had attended his church.