When is it necessary to use "have had"?

"Have had" is using the verb have in the present perfect tense.

Consider the present tense sentence:

I have a lot of homework.

This means that I have a lot of homework now.

On the other hand, we use the present perfect tense to describe an event from the past that has some connection to the present. Compare the following two sentences:

• I had a lot of homework this week.
• I have had a lot of homework this week.

If I only say had, this means that "having a lot of homework this week" is a completed event, either because there is no expectation of more homework, or because the week is over.

If I say "have had", I connect the event to the present, so it is possible that I might have more homework, and I could say something like this on, e.g., a Wednesday (in the middle of the week).

Another example will illustrate the importance of the connection to now:

• I had a lot of homework last year.
• *I have had a lot of homework last year. (this sentence is bad!)

In the first sentence here, using had, the sentence is fine. But using "have had", the sentence is ungrammatical, because "last year" is always a completed event that is not connected to the present. But, as we know, the present perfect tense means that there is a connection to the present. So, the sentence sounds wrong, because the verb and the time are contradicting each other.

We might think about a bit of logic. If we memorize phrases, we may fail to comprehend what meaning there is for grammar to bring. :)

Have can be a head verb.

I HAVE a book. (I own a book.)

I HAVE fresh strawberries at least once a week. (I eat strawberries.)

Have can be an auxiliary.

I have HAD this book for twenty years. I keep returning to it.

I have HAD fresh strawberries every week, for half a year. My cholesterol is lower.

Compare the Causative:

I have HAD my copy of the book replaced. Twenty years is some wear and tear. (I've had it printed on demand)

I have HAD fresh strawberries pre-ordered with my weekly shopping. (The shop assistant suggested it.)

For the bit of logic, we can think about a time frame.

I HAVE a book. (I close my time frame on the Present. I consider the Present.)

I have HAD a book. (I open the time frame. I consider the Present and the Past, some 20 years ago.)

I have HAD the book replaced. (My time frame is open.)

I HAD the book replaced. (My time frame is closed on the Past.)

This way, we learn about the structure of language, not select patterns only. If you would be interested, step-by-step:

CHAPTER 6. TO CHOOSE OWN PATH IN TIME

"I had a lot of homework this week." - past simple of have meaning the homework for this week is finished.

"I have a lot of homework this week." - present simple of have meaning the homework for this week, up to now, is unfinished.

"I have had a lot of homework this week." - present perfect of have meaning the homework for this week, up to now, is finished.

If you were asked whether you have ever had an accident while driving, you might answer that you had a couple of accidents when you were younger. It is of course the past tense. If you reported this conversation, you could say that you told him that you have had past accidents. It is sometimes called the past perfect tense.