M.J. Hyland, who authored the acclaimed 2003 novel How the Light Gets In, is often praised to be a subtle and complex portrayer of human psychology.
Is this sentence in perfect present or simple past tense? Why is it not : M.J Hyland, who has authored the acclaimed novel…
Thanks in advance! 
Present perfect generally indicates a continuing state. E.g., I have been a teacher for thirty years. This means that I was a teacher and I still am.
It is common to read things like, “Jones has written a book” while the book is still new – recently published, about to be published. But when a few years pass, we use the simple past for that.
Present perfect can also be used for completed past actions without a specific time reference.
OKAY:
I have eaten lengua tacos.
WRONG:
I have eaten lengua tacos last night.
OKAY:
I ate lengua tacos last night.
Since the original sentence has a year (“2003”), present perfect is inadmissible.
Okay, I understand now. So is it okay for a non-essential clause to be written in past tense, while the rest of the sentence is in present tense, as in the sentence above?
Thanks!
Sure: My dachshund Larry, who marked his territory earlier in the day, is casually surveying his domain.
Thank you!
My pleasure–hope it helps!