have
The verb have has two different functions in English, and the reduction or contraction of its forms depend on which of these functions is being expessed:
1
possessive have
One function of the verb have is that of expressing possession or ownership. In American English, this is always expressed with full forms have, has, had, which can be given their full pronunciation [hæ:v, hæ:z, hæ:d], or be reduced to [hɛv, hɛz, hɛd] in more rapid speech when unstressed.
This contrasts with British English, where these forms are often contracted to say, for instance, We've no time, which would sound unnatural in American English. One exception is the phrase you've no idea, which Americans do occasionally use.
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In the following examples, we see that with the meaning of possession, the forms of have aren't contracted in writing or speech, although they may be reduced to [ɛ] in natural to rapid speech. I'll say it once at a slow, deliberate speed with full forms, and then at a rapid conversational speed with reductions.____________
I come from a long line of animal lovers; I have a dog, my sister has a cat, my brother has a parrot...
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Note that as a past participle, had is always given it's full pronunciation has/have/had had [hæ:d].____________
I love dogs. I've had them all my life and I have one now that I adore.
2
perfective have
Another function of have is that of an auxiliary verb used in forming the perfect tenses. Here, the forms of have have three levels of reduction:
⦿ They're given their full pronunciation [hæ:v, hæ:z, hæ:d] when emphasized: I have seen it!
⦿ Original [æ] is often reduced to a short, whispered [ɛ] after a word with primary or secondary stress: Andy hăd called him two days earlier. (See also 'd [2])
⦿ They're fully contracted to 've, 'd, 's when both the host word and the form of have are both totally unstressed: I've called him, he just won't answer.
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In the following example from 002: Bird Watching, we see two levels of reduction for has. In the first instance, the phrase has added follows the (secondary) stressed noun bird watching and thus has is reduced. In the second instance, it's fully contracted to the pronoun it.____________
In other words, meeting Roman and getting into bird watching hăs added another dimension to my life. But more importantly, it's taught me that if we're open to new experiences, we can learn something new from almost everyone we meet.
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In speech, the present perfect auxiliaries has and have tend to be contracted more often than they're reduced, whereas the past perfect had, is more commonly just reduced. For instance, in the following example, it would sound a little robotic to say I have or even I hăve in the present perfect. However, in the past perfect example, it's the reduced form I hăd that sounds the most natural, whereas the contracted form I'd would sound a bit strange. The contracted 'd sounds better as part of a totally unstressed phrase, like if I'd called him.I've called him, I've texted him, and he just doesn't respond.
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I hăd called him, I hăd texted him, and he just didn't respond.
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I'm sure thạt ịf Ị’d called him, he would've responded.