Hello! This subject (i think i just used that word wrong, please correct me if i did) has been confusing me a bit for a while, and i could'nt find any information about this on internet so if someone can explain this to me it would be really helpful.
After reading your post, I realised that I say "I'd've" quite a lot in my actual speech. But I have never ever written it down, nor have I seen it written down (or, more accurately, I don't recall having ever seen it written down.)
It's not the kind of thing that I'd feel comfortable putting into a business email, definitely not an essay (unless that was my topic, oh, and I think that will be the topic of my next essay now.)
But it is the sort of thing which would fit nicely in the dialogue inside a novel. And you never know, it could one day be perfectly cromulent to write that, and would perhaps embiggen the written English language.
There are 49 incidences of I’d’ve in the Corpus of Contemporary American English (search for I 'd 've). All but one occur in dialogue in fiction. The other one was in a transcript of Oprah.
It doesn’t appear that I’d’ve has any substantial contemporary usage in nonfiction writing at any level of formality. Of course, people say I’d’ve all the time, but if they were to write it down, they’d probably write I’d have.
It is just the contracted form.
Contracted forms are not used when verb has its own meaning.
— I have my homework. (have stands for possession.)
—I've my homework.
— I have finished my homework. (have is an auxiliary.)
They are not used in short answers:
— Have you done your homework?
— Yes, I have.Yes, I've.
Also, when writing formal stuff, you normally use non-contracted forms. For instance, in an essay.
There's a difference in spoken English when you stress the non-contracted form. Compare:
— I've finished my homework.
(Standard statement.)
— I have finished my homework.
(Emphasis when speaking.)
You can't use pronoun-auxiliary contractions if they're final in a sentence
(so they can't be used in tag questions, for instance).
In general, if it's unstressed -- which is the norm, and a good reason for contraction -- a pronoun subject will be contracted with an auxiliary if there is one. The more stress the pronoun has, the less likely it is to be contracted with an auxiliary. The faster you're talking, the more likely it is. English speakers make decisions like this every time they open their mouths, automatically.
Since it's hard to stress pronouns (the reason we use pronouns is to avoid extra stressed syllables), it's almost universal to contract pronoun subjects and auxiliary verbs in English,
unless the auxiliary verb is already contracted with another word, like isn't.
In writing, of course, there is no good way to represent contractions.
Only apostrophes,
which are problematic -- they don't represent English, just typography.
They're, their, and there, for instance, are pronounced identically in English;
however, English speakers never feel confused about what they mean.
Only about how to spell them.