Is the word "I'd've" considered proper grammar?

I’ve’rd it u’db’f’re, so why n’t?

It’s acceptable. Since “I would have” is a personal statement, it is not something one would use in formal writing. With that in mind, the acceptable contraction is also not something one would us in formal writing.

Double contractions are most likely considered informal and non-standard.

I find myself using words like “wouldn’t’ve” and “shouldn’t’ve” but I don’t think I would use them in an essay. They might become more acceptable in future years, though. :)

I’d certainly say it, but I probably wouldn’t write it, even casually. It would have no place in formal writing, of course.

From a strictly grammatical point of view, though, I don’t see that it breaks any rule.

I used “I’d’ve” before on fluther (once), but I don’t think I’d’ve used it in a more formal setting though. English is a living, breathing language, and the boundaries of what is, and what can be, bend. Contraction derivation use happens. New words and new forms of words happen. There is room for invention in English. But I don’t know much about grammar, I’m just a poet.

It’s informal but it’s grammatically correct.

That’s the way I speak but it looks very clumsy when written. I’ve never seen this contraction in print.

Indeed, it is. As is “I’d’nt’ve”, “I’ll’nt’ve”, “we’d’nt’ve” and all other variations thereof.

I take great joy in using such contractions.

Not trying to be funny or smart aleck, but does Microsoft Word green or red line it? Microsoft Word usually researches online if the word you typed is used correctly. That’s why most college online courses require you to use Word first before you post your work.

If you wrote it on your resume I wouldn’t give you a interview.

I would never use it when writing, unless I was writing what a character said. Not even in a very nonformal communication would I use it in writing, but saying it seems ok when in a casual setting.

@johnpowell :Shouldn’t’ve been If you wrote it on your resume I wouldn’t give you an interview.

I’d have looks more ‘clean’ to me.
Or I’ld have.

Ditto downtide’s comment.

Spoken language can be very different from written language, and I think that the two should be kept separate. I would guess that most people would say “more and more” as sounding like “more’n more.” When I went to college, around meal time people tended to ask something that came out as “J’eat jet?”

@LostInParadise There are quite a few things like this. If someone I knew when to the shops, I’d ask “Chuhget?”, but I’d probably write this as “What’d you get?”.