I came across many sentences which have has had, had had for example
The one that has had the most profound impact is generics
I wanted to know what are the basic rule of using those?
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Sign up to join this communityI came across many sentences which have has had, had had for example
The one that has had the most profound impact is generics
I wanted to know what are the basic rule of using those?
Have is a helping or auxillary verb that can be placed in front of the past participle form to make all the perfect tenses.
I have gone to the store.
I had shown him the way.
I will have done this by the time he gets here.
The verb have itself is not exempt from this. There is the have {noun} where X is an object, and have {infinitive} which mean different things, but if you want to use a perfect tense with either one, you still put another have in front of it.
So have had, has had, had had can be valid.
It gets really fun with have to have.
I have 2 pieces of candy.
I have had 2,000 pieces of candy before.
She's (she has) had to take care of him in the past.
I had to help him otherwise my mom would have punished me.
I'd had quite an adventure when I traveled to Mexico.
He told me last month I'd had to have 300 dollars, but I only had 200. So I avoided talking to him.
I'll have had to have 3 sessions with the doctor by the time next year comes around.
I would have had to go with them but they canceled.
Perhaps this website about the perfect tenses helps. http://englishstandarts.blogspot.de/2012/01/perfect-tenses.html
A pity that English conjugation tables never show conditional perfect (would have done).
"I have had3, /he has had3" is pres. perfect simple. "had3" is the third base form or the past participle. The base forms are have/had/had.
"I had2 had3" is past perfect simple. "had2" is the second base form.
Has had/have had is actually present perfect, and it has its relevance with the present.Had had is actually past perfect, and it has no relevance with the present.
Has had is in the past perfect progressive tense. Basically, it indicates an ongoing action in the past, similar to past continuous, that was completed before some other action. In this sentence, it means that in the past generics had the most profound impact on the subject.