Student or Learner
I was asked to help explain the answer to a question. It comes from a testing paper for high school students in China. The question goes like this:
I had never thought about the form of a question tag in a sentence where the "should have + past participle" structure is used. So I referred to my Practical English Usage (International Student's Edition) and a few online sources including a related wikipedia page. It seems all of them pointed to the same solution, as Micheal Swan says in his Practical English Usage:If the main sentence has an auxiliary verb ... , this is repeated in the question tag. So I chose C.They should have informed you of the result of the competition by the time it was eventually given out, ___________?
A. haven't they B. didn't they C. shouldn't they D. hadn't they
Much to my surprise, I was told the correct answer should be D. I was then given the "official" explanation. It claims that when it comes to a question tag in a sentence where subjunctive mood is used, the actual auxiliary verb, as the question maker calls it, should be used, which in this case is not should. Because the time for what should have happened is before "it was given out", or, in other words, a past action. "They should have informed", as a sentence depicting a past event, is in fact one in the past perfect tense. Hence the choice of D as the correct answer.
In a way, this explanation seems to make sense. But a friends and I were suspicious of it. We referred to a few grammar books, including A Practical English Grammar, Cambridge Grammar of English, Oxford A-Z Grammar and Punctuation and Grammar for English Language Teachers and found nothing that supports the reasoning.
I would like to know if this is a grammar point that is not included in our books.
Is it possible that this is one of those questions where a non-native speaker got carried away and stretched out a bit too far in the interpretation of the grammar rules for a language they rarely use in actual life.
The explanation you were given is completely wrong. 'Should have informed' is not past perfect. There is no subjunctive in that sentence.
You chose the correct answer.