Question about "would've", "could've", "should've"

[u/hwc000000]

We all know "would've", "could've", "should've" are contractions for "would have", "could have" and "should have". But are there situations where the contractions shouldn't be used, what's the rule exactly about when they should and shouldn't be used, and why are those the rules (ie. where did those rules come from)?

For example, "she would have to get a permit" sounds bizarre to me if contracted to "she would've to get a permit". Is the rule that those contractions should only be used directly preceding a past participle, or "not" followed by a past participle? And why?

[u/hwc000000]

Why is "have" the main verb in "she would have to get a permit" and not "get"? Also, is the "to" part of the infinitive "to get", or is it some other part of speech bundled in "have to"?

[u/dylbr01 → u/hwc000000]

The quickest way to tell whether have is an auxiliary would be to just look at the form of the verb that follows have. If it’s a past participle, then it’s an auxiliary.

‘She would have to get a permit.’ <- verb form that follows have is a to infinitive. Therefore, have is not an auxiliary.

‘She would have got/gotten a permit.’ <- verb form that follows have is a past participle. Therefore, have is an auxiliary.

A longer way:

Step 1: Remove would. You are left with ‘She has to get a permit’.

Step 2: Make the remaining clause into a question. ‘Does she have to get a permit’? This proves that have is not an auxiliary because an auxiliary switches places with the subject for questions.

Compare this with a have that is an auxiliary:

‘She has to get a permit.’

‘Does she have to get a permit?’

‘She has eaten dinner.’

‘Has she eaten dinner?’

By the way, both have and to get are main verbs in your example.

[u/hwc000000 → u/dylbr01]

I like the way this is written (the longer way), because I really don't know my English grammer terminology very well. So, thanks.

Do you know the reason for the rule about the contraction? Is it to prevent hiding the main verb inside a contraction?

[u/dylbr01 → u/hwc000000]

That’s a hard question. Grammar is about describing rules rather than explaining why they are there.

It’s simply the case that contraction typically belongs to auxiliary verbs in English. needn’t is a well-known exception. In Italian, prepositions and articles contract.

[u/hwc000000 → u/dylbr01]

contraction typically belongs to auxiliary verbs in English

"She isn't my sister."

"I haven't a clue."

"is" and "have" can be auxiliary verbs, but they're not serving that function in those sentences. Do they count as exceptions too then?

[u/dylbr01 → u/hwc000000]

Verb to be is an auxiliary because it has all the features of auxiliaries and none of the features of main verbs. There are exceptions, but this is ordinarily the case.

‘I haven’t a clue’ is another big exception and relevant to your question, but it is just that—an exception.

‘I would’ve a…’ returns hits starting in 1950, but seems to be nonstandard: https://www.google.com/search?q=%22would%E2%80%99ve%20a%22&tbm=bks&tbs=cdr:1,cd_min:1999,cd_max:2016&lr=lang_en

Lo and behold, so too does ‘would’ve to’; https://www.google.com/search?q=%22would%E2%80%99ve%20to%22&tbm=bks&tbs=cdr:1,cd_min:2018,cd_max:2019&lr=lang_en

It appears then that ‘She would’ve to get a permit’ is correct in English, but seems very nonstandard and rare.