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if only we had . . .
Why not have ?

i had no idea . . .
Why not have ?

they have yet to identify . . .

Why not had ?

I really got confused when to use had and have.

Here is my thoughts, correct me if I'm wrong.

1)We use have when we own something right now, and we use had when we don't own something anymore.
2)Had is past tense, it describes something as it looked in the past.

And please take a look at another 'Have' question I've. Emotion: stick out tongue
http://www.EnglishForward.com/English/IGotAQuestion/2/xbpzw/Post.htm
Comments  
Hi Lokon,
lokonif only we had . . .
Why not have ?
The phrase 'if only' introduces a counterfactual or unreal condition, so you need the subjunctive form of the verb 'have', which is 'had'.
lokoni had no idea . . .
Why not have ?
You can also use 'have'. It depends on what you mean. If you use 'had', you are talking about the past. If you use 'have', you are talking about the present.
lokonthey have yet to identify . . .
Why not had ?
You can also use 'had'. It depends on the context. If you use 'had', there is a past context. If you use 'have', you are talking about the present.
Thanks.

What is difference between these two?

I've been though. . .

I'd been though. . .

Also, can I use I'd for things that happened today, like :
I'd soon forgotten . . .
Students: Are you brave enough to let our tutors analyse your pronunciation?
Do you mean "been through"?

I've been ... considers time up to the present moment.
I'd been ... considers time up to a moment in the past.

CJ
lokoncan I use I'd for things that happened today, like :
I'd soon forgotten . . .
Whether it was today or not has nothing to do with it.

I'd ... forgotten ... considers the forgetting only up to a moment in the past -- generally whatever moment in the past your conversation has been focusing on at the time you make this statement.

CJ
if only we had . . . [Remoteness from reality.]

i had no idea . . . [Remoteness from the time of speaking.]

they have yet to identify . . . [yet means still. We're waiting for a future event of identification.]

CJ
Students: We have free audio pronunciation exercises.
Thanks !