[Grammar] I didn't know there are/were so many.

[Edwalker]

Hello.

The following sounds fine to me with either "are" or "were":

My company has five manufacturing plants in the UK. I didn't know there are/were so many.

I'd say "were" seems most natural, but could somebody explain why we use past tense here please? Is it simply because we are referring to the past with "didn't"?

If so, is the version with "are" incorrect?

Thank you.

 

[5jj]

With reported speech/thought, backshifting is always correct if if the introductory verb is in a past tense.

If the situation reported is still true at the time of reporting, then backshifting is not essential.