[Grammar] to 'be' or not to 'be'

I have a simple question.
There is a sentence "They have been writing yesterday".
It sounded wrong to me, so I corrected it to "They were writing yesterday", but it seemed incomplete.
So I thought I should use simple past and say "They had been writing yesterday". Am I using the correct tense?

The more and more I read it, it all starts sounding the same.

"They were writing yesterday" is correct as a standalone sentence.

"They have been writing yesterday" is incorrect.
"They had been writing yesterday" is incorrect.

Can you post the appropriate tenses as well? That would be helpful for further research.
Thank you for giving a very clear answer.

Grammar is confusing said:

Can you post the appropriate tenses as well? That would be helpful for further research.
Thank you for giving a very clear answer.

Click to expand...

Are you asking us to tell you what tenses "They were", "They have been" and "They had been" are? I realise that your username gives us a clue as to how you feel about grammar but you need to understand that we are not here to replace your own hard work and study. There are multiple ways for you to find out which tenses they are. Let us know what you find out.

They were - Past continuous/past progressive.
They have been - present perfect
They had been - past perfect

It was relatively easy for me to find it. But I don't have a grammar book with me and I am forced to rely on the internet. My friend who knows a lot more about grammar than I do said "We use the past continuous to say that somebody was in the middle of doing something at a certain time. The action or situation had already started before this time but had not finished”. That is why I got confused and said "They were shopping yesterday" might be wrong.
He also suggested that I use simple past instead.

I am not a native speaker of English and I was not taught grammar in detail at school. Reading words such as past continuous and past progressive have confused me a lot before. The only reason I posted this query here was to confirm what he said and to get a teacher to explain when it was appropriate to use which, with examples, as I was unable to relate the examples that I read elsewhere with this sentence, because somewhere I felt this sentence sounded wrong. Which lead me to realise that I didn't have a good grasp of the concept. But as you suggested, I shall do more studying and try to learn grammar.

Hello, Grammar is confusing!

Yesterday is in the past, so you need to use the past tense.

Grammar is confusing said:

"They were shopping yesterday" might be wrong.

Click to expand...

I would say something like 'They were shopping yesterday when I called one of them', but I am not a teacher.

Thank you for answering. I understand that yesterday is in the past.
And yes, I would also not leave sentences like 'They were writing yesterday' and 'They were shopping yesterday' as standalone sentences.
But as emsr2d2 pointed out, that is the only option that can work that way.

The problem was that none of the examples that I read left the sentences so abruptly; hence the mix-up.
The confusion is now cleared.
Thank you Matthew Wai, emsr2d2 and tzfujimino!

Grammar is confusing said:

I would also not leave sentences like 'They were writing yesterday' and 'They were shopping yesterday' as standalone sentences.

Click to expand...

If they were standalone sentences, I would think that they were writing/shopping all day, but I am not a teacher.

Grammar is confusing said:

Thank you Matthew Wai

Click to expand...

You are welcome.

Grammar is confusing said:

I have a simple question.
There is a sentence "They have been writing yesterday".
It sounded wrong to me, so I corrected it to "They were writing yesterday", but it seemed incomplete.
So I thought I should use simple past and say "They had been writing yesterday". Am I using the correct tense?

The more and more I read it, it all starts sounding the same.

Click to expand...

The title of your tread has nothing to do with the content. Please create better titles in the future.

MikeNewYork said:

The title of your tread has nothing to do with the content. Please create better titles in the future.

Click to expand...

I wrote that because of the verb 'to be'. And yes, the title is misleading, I shall fix that in the future.