When they mean would have? Do they sound similar? I would of course understand if it were a sentence like this, but misusing it is puzzling.
Would have becomes would’ve
would’ve becomes would of
ETA: yes, they sound similar enough in some accents/dialects for the above to happen.
I guess I sound like I’m saying “wood of” and it’s a contraction of “would have” and when I write it, it’s would’ve.
“Would’ve” sounds a lot like “would of”. Unless I deliberately enunciate clearly when I say “piece of paper” the “of” sounds the same as the “'ve” in “would’ve”. Personally I find “would of” annoying and I’m not excusing it but it’s not hard to see why people would say it.
I personally just use woulda. 
People say all kinds of things in normal speech. That is, everyone of us pronounces words differently than we “think” we’re pronouncing them, every time we open our mouths. It is rare that any of us are ever aware of this.
Now, you have come across an example of a word where the usual pronunciation, in a certain phrase when spoken in normal (not slow, careful, self-conscious) speech, happens to sound exactly like a DIFFERENT word (again, when spoken in normal speech) – one which happens to also be an unstressed part of certain common phrases. So, this happens to be one of those few times when some folks make the mistake of WRITING one word when they mean the other.
So, really, your question is “why do people sometimes WRITE ‘of’ when they should write ‘have’?”. Because all of us SAY things like this, all the time. It takes special circumstances for this common, normal fact (not a “mistake”) to be revealed in writing (where it IS a mistake – though this kind of thing does sometimes change the language itself, rather like how “fneosan” became “sneeze”).
My theory is that bad spellers don’t usually tend to be readers. (I said usually, there are other reasons, I know.) Readers see the words constantly. Non-readers are just hearing the words so interpret them as they hear with creative spelling, e.g. ‘would of’ and ‘rediculous.’
What I want to know is, why do people say “would of/have” (sloppy pronunciation) instead of “Had”, i.e.: “If I would have gone yesterday” instead of the correct “If I had gone yesterday”?
To emphasize the conditional nature of the thought.
I wouldn’t say this is about spelling. It’s sloppy usage and illogical thinking.
For all intensive purposes, “would’ve” and “would of” sound the same.
I would of never made this mistake.
I think you meant to say, “I had never of made this mistake.”
English is a time stressed language. Words that are less important to the meaning of a sentence, like auxilliary verbs, are sped up, unstressed, and even slurred. I taught English overseas for awhile and this is really confusing to new learners. “I’m going to the store,” for example, but “I’m gonna see a movie.” “I can …”, unless you’re emphasizing it is, “i-cun”. And “would have” is “would’ve”. Native speakers are often unaware they’re doing this.
Oh ok, I find it really strange because I don’t pronounce them the same, just like there their they’re or your you’re. Can’t imagine how they sound the same really. Need to pay more attention.
I could care less
FWIW, when it is contracted to would’ve in my accent it sounds identical to “would’f” so I can easily see why, when people write it out longhand they may get it wrong.
Are you saying you pronounce their, they’re & *there *differently? That’s bizarre. I’ve never heard of that. What kind of accent do you have?
Don’t fret about it. Nothing quite so weird and inconsistent as English language pronunciation and if you haven’t come across too many different accents and dialects then it can be difficult to appreciate what differences are out there.
And nothing annoys me more than anyone trying to suggest that there is a “correct” pronunciation of any English word. It is a living language, mongrelised and twisted throughout history. Gloriously ever-changing it means we have to accept those Shakespearean “moonbeams” equally alongside monstrosities such as “medalled”
FWIW I’m from the North-East of England and “there, their, they’re” and “your, you’re, yaw” are all pronounced the same. Whereas that classic “Mary, merry, marry” are all very different. (but go 40 miles in any direction and that will probably change).
Well, in the worse case scenario, they do.
(By the way, these kind of slip-ups are called eggcorns.)
When I used to teach English as a Second Language in Europe, I used to have to teach a lot of incorrect usage that is common to native speakers.
“I gotta go 'cause I wanna see a film and it’s gonna start in 10 minutes.”
gotta
wanna
gonna
shoulda (should of)
woulda (would of)
coulda (could of)
Yes, all crappy English, but if you want your students to understand when people speak quickly, you have to teach them that too. I did stress they should never write that way.
Same goes for the typical wrong answer people give to the question:
“Do you mind if I borrow your pen?”
“Sure.”
If you have no problem lending the pen, the correct answer would be “No” meaning in the negative, “No, I don’t mind.”
However, most people answer in the positive, even though they mean the negative.