Ndtyhij

"Would of" is a garden variety malapropism (Wikipedia - Malapropism).

Some more interesting malapropisms are "tantrum bicycle" instead of tandem bicycle, "Alcoholics Unanimous" instead of Alcoholics Anonymous, "a vast suppository of information" instead of repository of information, "Miss-Marple-ism" instead of malapropism¹ and Mike Tyson's "I might fade into Bolivian" instead of oblivion (these are all borrowed from that same Wikipedia article).

The basic idea is that no one has perfect knowledge of any language, not even the ones they speak natively. We hear things incorrectly and then repeat the mistake.

We know that English speakers often contract "would have" into "would've." This is pronounced identically (in some dialects) to "would of," so the mistake is easy to make.

¹ This one seems too perfect to be a complete mistake. The "miss" sound is totally absent from "malapropism" and the term, for those who didn't follow the Wikipedia link, comes from a character named Mrs Malaprop. It seems unlikely that the supposed speaker of "Miss-Marple-ism" wasn't aware, at least subconsciously, of the correct word, or at least its origins. In which case, this neologism may really be an eggcorn.

This is probably a case of hearing a phrase and assuming/guessing how it should be spelled. Would have can be abbreviated as would've, and in rapid conversation, the pronunciation of "would've" is basically the same as "would of."

Great question. I also get annoyed when I see this phrase, especially from people who should know better. At one of my old jobs year ago, I worked with an account manager who actually used that phrase in an e-mail, saying something like "I should of known better". Yes, an account manager "should of" had a better education to know proper grammar... or at least know that's not a phrase used by professionals.

Even though the phrase might be pronounced and heard as "should of" (or "would of" or "could of"), there's no such phrase in written English. No school that I've heard of teaches this phrase and basic rules of grammar "abbreviate the word have as 've".
And writing "should of" takes just as many characters to write as "should've", so it's not like it's text-speak.

In my opinion, it's people being stupid, ignorant, or trying to be funny/ hip/ trendy by using the wrong phrase. Then other people see it and want to be in on the joke, so they use it also.

This has been answered better than I could even aspire to. However, I thought it would be interesting to realise that the same people who use (whether in speech or writing) the term 'would of' also constantly, and usually, does the same with 'could of', 'there' - instead of 'their' and 'then' instead of 'than'. This makes it hard for me to believe that it is mondegreen, since these are basic English building blocks, and no school would teach this to even allow for misinterpretation or mishearing. Surely pupils must also write, and teachers check the spelling?

To me, it's interesting, because it is commonly found on forums and popular social video website comments and as such, the perpetrators do not deal well with friendly correction from others :-)

The real question here seems to be not "how does this error happen?", because it's easy to see how you could mistake two similar-sounding words, but rather "how is it possible that this glaring error has become so ubiquitous in the last few years, even in texts written by native speakers and people in higher education?"

People are now much more likely to seek news, information and entertainment on social media, blogs and sites with user-generated content like Stack Exchange, instead of in books, magazines and newspapers. (Whether this evolution is inherently good or bad is a different discussion). This means that people are now regularly exposed to non-professional writing, with no editor between the writer and the "publish" button. The fact that writers and news media are increasingly building a social media and internet presence, and bloggers and social media content creators are becoming more professional, is also blurring the line between professional and non-professional writing.

As a result of this, errors in spelling or grammar can spread rapidly, much like other forms of misinformation. Unless there is a turnaround in reading habits, or a new concept of reputable sources of language use in the online world emerges, or schools start to specifically target this problem, I cannot see the phenomenon of "viral" language errors going away any time soon.

What most of you are missing is that "of" is preposition, and prepositions are slippery beasts. The "rules" for prepositions are complex and, for most people, in large part incomprehensible.

While an English purist would quickly cry "foul!", someone with, say, a 5th-grade education might easily believe (without applying much critical thought) that, in "If I had the time I would of eaten sooner", "of eaten sooner" is a prepositional phrase which somehow modifies "I would".

They are speaking/writing without applying an English teacher's "starch", and to them it makes perfect sense. After all, that's how (they think) their parents speak.