I am not without my regrets. I mean, I’d be a millionaire many times over if I’d seen Bitcoin coming. And I probably shouldn’t have gone to see “Prometheus.” (It’s just a thinly veiled remake of “Aliens.” Come on, Ridley!) Oh well … could of, should of, would of, right?

Wrong.

I see this error frequently. Folks incorrectly substitute “of” for “have” in phrases such as “I could have done better” or “I should have seen that coming.”

It’s easy to understand where the confusion comes from. In speech, we often shorten “should have” and the like to “should’ve,” which sounds like “should of.” The misheard conjunction then makes its way back into writing, and we have ourselves a grammar error.

Beyond just saying it’s wrong, though, let’s look at why it’s wrong. “Should,” “would” and “could” are auxiliary verbs, or helping verbs. Their function is to augment the main verb (i.e., to “help” it). They can be used to add a tense or aspect to a verb – as we’ve learned how to do recently with the perfect and progressive forms – or to change a verb’s modality into the conditional mood. We haven’t talked about moods in the grammatical sense yet, so we’ll leave it at that for now.

When using an auxiliary verb, you need a main verb for it to augment – something like “go,” “be” or “have.” As a preposition, “of” doesn’t fit the bill. It leaves our helping verb with nothing to help and starts a prepositional phrase to nowhere.

To wrap this rule up: Should you use “of” after an auxiliary verb? No. Would I recommend investing in Bitcoin? I advise against taking any investing advice from your grammar columnist. Could I forgive Ridley Scott for “Prometheus?” Yes … but only because he made “Blade Runner.”