Present perfect vs simple past vs past perfect

English as a Second Language English Vocabulary, Grammar and Idioms
1

Dear teachers,

Let’s consider these 2 cases:

Case 1. The morning is over:

  1. I haven’t seen him since he left this morning.
  2. I haven’t seen him since he had left this morning.
  3. I haven’t seen him since he has left this morning.

What is the correct sentence? What is the rule?

Case 2. It is still morning.

  1. I haven’t seen him since he left this morning.
  2. I haven’t seen him since he had left this morning.
  3. I haven’t seen him since he has left this morning.

What is the correct sentence? What is the rule?

Thanks
Quoc

PS: I can’t give my idea because I don’t know.

2

.
The key is that he left– it is a finished event-- and the since clause indicates a reference point in (past) time. Since also clearly orders the two events chronologically.

Therefore, only 1 and 4 are reasonable choices.
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