Prepositions are handy things, cementing the relationship between parts of a sentence. In the sentence “He was caught between a rock and a hard place,” for example, the preposition “between” connects his predicament and the site of his predicament. In “She won’t come out from under the table, the preposition “under” connects her refusal with the place she’s refusing to vacate.
One preposition seems to create more problems than others: “of” thee I sing.
As Merriam-Webster says in its entry, “of” indicates a relationship of “belonging to, relating to, or connected with (someone or something),” as in “the problems of Volkswagen”; indicates “that someone or something belongs to a group of people or things,” as in “a flock of pigeons”; or indicates someone or something “living or occurring in (a specified country, city, town, etc.),” as in “Robin of Locksley.”
But using “of” invites flabby writing. “The chairman of the board of directors,” for example, is just a long way of saying “board chairman.” “Because of the fact” and “in spite of the fact” are just long ways of saying “because” or “despite.”
Garner’s Modern American Usage warns against the “virus” of “of,” saying: “The only suitable vaccination is to cultivate a hearty skepticism about its utility in any given context. If it proves itself, fine. Often, though, it will merely breed verbosity.”
Perhaps the most insidious appearance of “of,” though, is in places where it’s not wanted, or needed.
“We could of won if we had concentrated better,” for example, is a common problem of transcription, for want of a better word. What the person probably said was “We could have won,” or “We could’ve won,” the contraction of “could” and “have.” Garner’s says people who use “of” when they should have used “have” are “semiliterate,” though some highly literate people have done so.
Sometimes it’s hard to tell if “of” is welcome or just excess baggage, which may lead to people erring on the side of inclusion. “It happened in December of 1942,” for example, has no need of “of”; “It happened in December 1942” is perfectly fine. Yet it’s fine, and more idiomatic, to say “in the spring of last year,” rather than “in spring last year.” (That, of course, assumes there is some reason for not just saying “last spring” and be done with it.)
Most usage authorities to still want you to include “of” in phrases like “a couple of things” instead of “a couple things,” though the absence of “of” there is creeping into idiom. (Garner’s lists it at Stage 3 of the five-stage Language-Change Index and notes, “This shift in usage may be fully acceptable someday.” Just not yet.)
More recently, though, “of” has been showing up in expressions like “that’s not too big of a deal,” “that’s not enough of a salary to justify my jumping ship,” and “that’s as big of a problem as I ever want to encounter.” That usage is considered colloquial, nonstandard, or just plain wrong. The American Heritage Guide to Contemporary Usage and Style, published in 2005, says that in these cases, “of appears between an adjective and the noun phrase it qualifies as part of phrases that specified degrees of difference or equality, as in How big of a job or was it?.” It notes that that usage is too colloquial to appear in formal writing.
In nearly every case, questionable uses of “of” can be corrected with only a slight move of a cursor.
If all of this is too big of a lesson to swallow, you should of studied more in English class.