What is the difference between "had had to" and "have had to"? Please provide examples and elaborate explanations. What do each mean in the sentence?
- have had to
- had had to
These are both perfect constructions, which you may read about in stupefying (yet inadequate) detail here.
The perfect is constructed with a form of HAVE as an auxiliary verb followed by the past participle of the lexical verb. In these cases, the lexical verb is also HAVE, employed in the construction HAVE to ≈ must. The past participle of HAVE is had, so these constructions end with had to. In have had to ... the auxiliary is cast in the present-tense form, which is have with a first-person subject, so this is a present perfect. In had had to ... the auxiliary is cast in the past-tense form, which is always had, so this is a past perfect.
Examples of the use of these constructions:
I have had to explain the perfect construction many times.
When I say or write that sentence I mean that explaining the perfect construction many times is a component of my present history and experience.
Two minutes ago I wrote that I had had to explain the construction many times.
That sentence means that explaining the perfect construction many times was a component of my history and experience at that time in the past.
While StoneyB's expertise in answering such questions may sound too technical for a learner (especially a non-native), here I'd try to explain it at least in a simpler way, if not better!
Yes, it is difficult for non-native speakers to understand double verbs that too when they are sitting with each other!
Let's start with something very common what you and I fully understand. If I give you a chocolate to eat, you may say -
I eat a chocolate
But then, in good English we practice
I have a chocolate/breakfast etc.
This means those all items you eat.
So, be clear, we'll not use 'eat'. Instead, we'll use 'have': I eat breakfast = I have breakfast
Writing that again:
I have breakfast
Here, 'have' is used as a main verb. And, we are talking about the present situation i.e. present tense.
NOW, what if this present tense gets a little old matter? In other words, little time has passed and you want to tell that same sentence.
You know that it is called as 'present perfect' because here we connect the present thing with the recent past.
So, if you have breakfast at say - 8 am, and if you reveal it at 10 am or so, what do you say with our old tradiitional writing?
I have eaten breakfast
The entire sentence is now present perfect. You see that 'eat' here became 'eaten' because it's past (participle).
But as we discussed, we don't use 'eat'. Instead, our original word was 'have'. So, replace 'eaten' with the past participle of 'have' which in this case is 'had'
Tell me, what do we write now?
I have had breakfast.
Note that in this example, the main verb is again 'have' and not 'had' because 'had' is actually 'eaten' if you remember!
I think it'd be now easy for you to understand 'had had'.
The example is in past perfect.