Present perfect vs simple past vs past perfect

[Tung Quoc]

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.

4. I haven't seen him since he left this morning.
5. I haven't seen him since he had left this morning.
6. 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.

[Mister Micawber]

.
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.
.
_________________
Native English teacher at Mister Micawber's