This is a past perfect and is used to clarify the order of past events.

The following is correct:

James had had his hair cut when John walked in.

This means that the haircut took place prior to John entering.

Alex had had four glasses of wine when he was ejected from the bar

Again we know that the drinking took place prior to his being ejected.

If it said:

Alex had four glasses of wine when he was ejected from the bar.

this means that he was in possession of the four glasses when/as he was being ejected, which is a totally different meaning.

I hope those examples help.

@unlimitedgmat, can you please explain what is the difference b/w below 2 sentences:

he had had success broadcasting his controversial radio program on highly regulated terrestrial airwaves.

he had success broadcasting his controversial radio program on highly regulated terrestrial airwaves

hemant_rajput wrote:@unlimitedgmat, can you please explain what is the difference b/w below 2 sentences:

he had had success broadcasting his controversial radio program on highly regulated terrestrial airwaves.

he had success broadcasting his controversial radio program on highly regulated terrestrial airwaves

Hi Hemant,
In the above case:
2nd option is correct because if this is the only sentence then we will use only one had.
If we are appending other sentence which occurred after "he had success" then we will use had had to show that the above event occurred first.

1.Though he had had success broadcasting his controversial radio program on highly regulated terrestrial airwaves, Howard Stern opted out of terrestrial broadcasting in favor of the less regulated satellite radio medium.

2.Though he had success broadcasting his controversial radio program on highly regulated terrestrial airwaves, Howard Stern opted out of terrestrial broadcasting in favor of the less regulated satellite radio medium.

what is the difference in meaning of above 2 sentences?

hemant_rajput wrote:1.Though he had had success broadcasting his controversial radio program on highly regulated terrestrial airwaves, Howard Stern opted out of terrestrial broadcasting in favor of the less regulated satellite radio medium.

2.Though he had success broadcasting his controversial radio program on highly regulated terrestrial airwaves, Howard Stern opted out of terrestrial broadcasting in favor of the less regulated satellite radio medium.

what is the difference in meaning of above 2 sentences?

2nd sentence here is wrong as it is not clear which one occurred first. He had success first and then he opted out or he opted out first and then he had success. To clear this doubt our 1st sentence is correct that is : "Though he had had success" which means he had success first and then he opted out.

The use of past perfect here is to show the timeline of two past events. Past perfect is used for the event that happened first - "success broadcasting his controversial radio program on highly regulated terrestrial airwaves". Simple Past is used for the event that happened after the first event - "opted out of terrestrial broadcasting in favor of the less regulated satellite radio medium"

so "Had Had" is necessary here to show the event occurred first.

let me know if you have any doubts regarding this.

Yes, it is appropriate to use "had had" and no, it's not redundant.

Have and its past tense and participle form had can have two equally valid uses -- as a main verb [as in "She had a bad headache earlier"] and as an auxiliary (also known as helping) verb [as in "She had given him more than enough chances already"], where the verb had is the "perfect" auxiliary verb to the main verb gave, seen in its participle form here, given.

Ok. Good. So what?

Well, it turns out that once in a great big while it is possible to use the main verb have simulataneously with the auxiliary verb have and to say something like "had had."

That is perfectly fine. Honest. Really. However, the reality is that many people think that such a construction is not euphonic (even though it is perfectly grammatical) and therefore avoid it.

Hope this helped you out.