Quote:
But i have read in manhattan SC book that had is not used if sentence contains some other term referring back to that time or helping in deciding the sequence of events such as before
here also i think previously establishes that point and hence there should be were instead of had
I'm not sure about the rule you're referring to in the Manhattan SC book, but here's an overview of the past perfect:
When a sentence discusses two completed actions, the past perfect (had + verb) can be used to refer to the action that occurred
first.
In some instances, either the simple past (preterit) or the past perfect can acceptably be used. In case of the latter, the past perfect merely serves to emphasize that one action occurred before the other. The sentence you are asking about falls into this category.
Simple Past: Literacy opened up entire realms of verifiable knowledge to ordinary men and women who
were previously considered incapable of discerning truth for themselves.
Past Perfect: Literacy opened up entire realms of verifiable knowledge to ordinary men and women who
had previously been considered incapable of discerning truth for themselves.
In the first version, the simple past emphasizes that both actions took place in the past.
In the second version, the past perfect emphasizes that one action took place before the other -- that ordinary men and women were considered incapable of discerning truth for themselves
before literacy became commonplace.
If anything, the word "previously" reinforces the acceptability of the past perfect here because it emphasizes the sequence of events.
In other instances, the past perfect is required, and the simple past
cannot be used.
For example, when dealing with hypothetical ("if") clauses and result clauses, the tenses follow a very strict pattern. If the main clause contains the past conditional (would have + past participle), the "if" clause must contain the past perfect.
Correct: Investors' concerns would have grown significantly if the market
had continued to decline.
Incorrect: Investors' concerns would have grown significantly if the market
continued to decline.
In this case, an adverb of time (e.g. "before" or "previously) would not normally appear in the same clause as the past perfect. That might be the rule you're thinking of.