Good Uses of Of
Of isn't always wrong though. It has good uses too, such as Please bring me a cup of coffee. You have to write it that way to show that you want the liquid to drink. If you tried to omit the of, you might end up with Please bring me a coffee cup, which has a different meaning. (Of course, you could always just say, “Please bring me a coffee.”)
I also find of to be useful when I'm dealing with a complex trail of possession. For example, I find it easier to follow something like He's the cousin of my neighbor's brother than He's my neighbor's brother's cousin.
Prepositions in Idioms
Finally, English has many idioms and set phrases that use prepositions. For example, even though you should generally exclude of when you can and it doesn’t change the meaning (you jump off a bridge, not off of a bridge), the correct phrase is a couple of something, not a couple something. You had a couple of meetings yesterday, not a couple meetings.
In general, you should avoid ending a sentence with a preposition when you can omit the preposition without changing the meaning of the sentence. For example, it’s better to ask someone, “Where are you?” than to ask, “Where are you at?” Nevertheless, the sentence It’s where it’s at, is an idiom that means “hip and cool” and requires the final at.
Search for Prepositions in Your Early Drafts
Although of and other prepositions can be useful, they can also clutter your writing. If overusing them is your writing tell, as it is mine, use your word processor’s "find" feature to search for specific prepositions after you've finished your first draft. If you find an of or an on every few sentences, you should probably do some rewriting.
This podcast originally appeared as an article in OfficePro Magazine.
Mignon Fogarty is better known as the host of the Grammar Girl podcast and author of seven books including the New York Times best-seller Grammar Girl's Quick and Dirty Tips for Better Writing. You can find her online at Twitter and Facebook.