What is the difference between:
1. I had been talking to her last week. (Past Perfect Continuous)
2. I was talking to her last week. (Past Continuous)
The first sentence was taken from a book by Dave Willis, "Rules, Patterns, and Words: Grammar and Lexis in English Language Teaching (Cambridge Language Teaching Library).
Magic791. I had been talking to her last week. (Past Perfect Continuous)
Past perfect tenses don't make sense without a previous context that establishes some action or event in the past, called the anchor. The past perfect then expresses the idea that an action or event happened before the anchor point in time. So this talking period happened before something else happened. Thus, past perfect tenses are dependent tenses. You cannot start a conversation with such tenses, for example.
We do not usually use adverbs of time that are measured from the time of speaking, however, when we use the past perfect tenses, so your sentence is unusual. Normally, we would say I had been talking to her the previous week. Here the time is measured from the anchor point.
Magic792. I was talking to her last week. (Past Continuous)
The past tenses are not dependent tenses. The anchor is by default the moment you say the sentence. So this talking period happened before the speaker says it.
CJ
I guess lack of context made the past perfect example strange because as you said, we need a reference point as the past perfect usually describes an action before another past point.
https://books.google.com.sa/books?id=3F8IMy5T8xMC&pg=PA100&lpg=PA100&dq=%22I+had+been+talking+to+her+last+week%22&source=bl&ots=0IYvZmA6zz&sig=ACfU3U19gL6wbQhzwlKRvRwBrjTRhGffQA&hl=en&sa=X&ved=2ahUKEwiG-_HR8d_9AhW7UKQEHQzxB1kQ6AF6BAgIEAM#v=onepage&q=%22I%20had%20been%20talking%20to%20her%20last%20week%22&f=false