Unlike

The past perfect tense can have a specific time unlike the present perfect tense.

Unlke the present perfect tense, the past perfect tense can have a specific time.

(Unlike part = the green words)

Yes, I think it's ok.

Hi

What do you mean by specific time? Can you give an example?

yes, 'unlike' is preposition in the sentence.

Present perfect - cannot have specific time with its usage.

I have been to the US last August --> Not ok.

Past perfect - can have a specific time

I had visited the US last August before I decided to buy a house there two months later. --> Ok

Present perfect - cannot have specific time with its usage.
I have been to the US last August --> Not ok.

Past perfect - can have a specific time
I had visited the US last August before I decided to buy a house there two months later. --> Ok

Past perfect - can have a specific time- Not really so

holydukePresent perfect - cannot have specific time with its usage.
...
Past perfect - can have a specific time
...These observations are correct. However, as vsuresh points out, the second example doesn't really need a past perfect at all, so a better example is needed. I would change your explanation a little:

The present perfect cannot be used to

vsureshShe had done the work when her father arrived. Here past perfect denotes the completion of the action but does not speccify when it was completed.

On the contrary, strange as it may seem, a when-clause is regarded as the mention of a specific time.

When had she done the work?

At 5 o'clock. |

Thank you CalifJim

Can you help me with this?

She had done the work when her father arrived.

This I thought does not denote a specific time as we know only that the work was completed before the second event- her father arriving.

(For example- She completed the work at 1 PM. Her father arrived at 9.)

vsureshThis I thought does not denote a specific time

True, it doesn't - not in the sense you're thinking about it. After all, it doesn't say she had done the work at 5:16:25 on 6-28-2011.

But for purposes of the grammar of the perfect tenses, a when-clause is specific enough for us to say that it can't co-occur with a present perfect (though

hmmm... So with before/after/prior to/by the time and the such, the order of the events are already given, so there is no particular need for the past perfect tense (so one could use the simple past --> leading to the usage of specific time)

but when is like another time given

CJ, can you check whether this example works as a specific time with past perfect?

I

holydukeCJ, can you check whether this example works as a specific time with past perfect?
I had completed the assignment when the clock struck 12.

It's "perfectly" fine.