A friend of mine who has learned English in the past 8 years or so asked me to please explain what "had had" meant and what "have had" was.

I could not. "You can mostly just ... say something else. It's horrible."

She found a helpful youTube video, don't worry.

@futurebird

For any ESL learners who are wondering:

The first word in each of those phrases is an auxiliary verb. If I say "I have eaten," have is an auxiliary verb that indicates that we're in the perfect tense, and eaten is a past participle, which specifies which action we're talking about. In "have had" — for example, "I have had a bath" — have is the auxiliary verb and had is the participle. The reason it's confusing is just that we have to forms of the verb have next to one another.

Now consider: "when you came home, I had already eaten." The second part of this sentence is in the pluperfect tense, and it expresses something that was already in the past when something else (that's in the past) happened. The pluperfect is, if you like, more past tense than the past tense. In the sentence "by the time you came in, I had had my dinner", the first had is the auxiliary verb, indicating the pluperfect tense, and the second had specifies the action. It would be easier to understand if I'd written "I had eaten my dinner" (where had is the auxiliary and eaten the past participle), but "I had had my dinner" is more idiomatic.

@CppGuy @futurebird This s a great explanation. English is a bit unusual in that auxilliary verbs ("had", “been", "was”, etc.) are habitually used to modify the tense of the main verb. Most other language modify the main verb to indicate tenses like pluperfect and imperfect.

@CppGuy @futurebird Fun fact! English only has two grammatical verb tenses: simple past, and simple present. I.e. “I walked" and “I walk". Every other verb tense is constructed from one or more auxiliaries, or inferred from context, e.g. in “tomorrow I walk to Biloxi", the walking happens in the future and has the same meaning "tomorrow I will walk to Biloxi”

@tobiaspatton @CppGuy

Sitting and thinking about things like:

"It had've been"
and
"It hadn't have bent"

Which people say all the time but are probably cursed.

@tobiaspatton @CppGuy

Sitting and thinking about things like:

"It had've been"
and
"It hadn't have bent"

Which people say all the time but are probably cursed.

@futurebird @tobiaspatton

Those aren't grammatical in my idiolect. The nearest might be something like "if you had been on time (or if you hadn't been late) it would have been easier to catch the bus." These refer to something that's both in the past and counterfactual.

Contrast with something that's in the present but also counterfactual: "if I were rich (or if I weren't broke) I would take a taxi".

Contrast again with something that's in the present or the future and not known to be counterfactual: "if it rains, we'll take the bus."

And something in the past but not known to be counterfactual: "if I've bored you to death with grammar, I'm sorry" or "if I was rude, I didn't mean to be."