If you don't mind my saying so

First of all, I just want to say that I appreciate you reading this post. You taking time out of your day to learn about grammar means a lot to me. It must get frustrating, me lecturing you all the time, so thanks for coming back. And thanks especially to the readers who haven’t given up on today’s post yet, despite me making the same grammatical mistake four times thus far.

Did you notice it? Don’t feel bad if you didn’t – it’s such a common error that it doesn't actually sound wrong to a lot of us. (By the way, Microsoft Word’s Spelling & Grammar tool didn’t pick it up either. Humans: 1; Robots: 0.) Here’s what I should have written:

First of all, I just want to say that I appreciate YOUR reading this post. YOUR taking time out of your day to learn about grammar means a lot to me. It must get frustrating, MY lecturing you all the time, so thanks for coming back. And thanks especially to the readers who haven’t given up on today’s post yet, despite MY making the same grammatical mistake four times thus far.

In technical terms, I should have been using the possessive case for the pronouns that are modifying gerunds. Let me explain.

What are gerunds?

A gerund (pronounced with a soft g, as in Jerry) is a verb form that functions like a noun. It is made by adding the suffix “-ing”: “read” beomes “reading”, take becomes “taking” and so on. What do I mean by “functions like a noun”? Well, do you remember learning in school that nouns are people, places or things? Gerunds are things – the gerund “reading” really means “the act of reading”; the gerund “taking” really means “the act of taking”. In the sentence “I read a book”, “read” is a verb, but in the sentence “I like reading”, “reading” is, for all intents and purposes, a noun – it could just as easily be replaced with “bananas” or “Hawaii” or “Mad Men”.

Why we use possessives with gerunds

"What's the deal with gerunds?"

Let’s go back to my earlier example: “I appreciate your reading this post.” Here, I’m not saying I appreciate you (although I do, you know). I’m saying I appreciate a particular act of yours – the act of reading this post. The same goes for all the other examples. “It must get frustrating, my lecturing you all the time.” You’re not frustrated by me, I hope; you’re frustrated by the lecturing that I do. It’s the same principle that would make us say “I’m a big fan of Jerry Seinfeld’s acting” rather than “I’m a big fan of Jerry Seinfeld acting”.

Beware of present participles

How about this sentence? “I smell coffee brewing.” You’d think, based on what we’ve learned so far, that it would be better to say “I smell coffee’s brewing”, but that’s obviously wrong. Here’s why: In this case, “brewing” isn’t actually a gerund. It’s a present participle ­– the only other verb form ending with “-ing”.

Present participles have many uses. They can indicate an action that is taking place continuously (“I am writing”) or two actions that are taking place simultaneously (“Shaking his head, he walked away”). They can also act as adjectives (“I edged away from the snarling dog”). And, most relevantly for today’s topic, they can be used after verbs of perception: “see”, “hear”, “smell” and “feel”. When we say “I saw her standing there”, “I hear children playing”, “I smell coffee brewing” or “I feel my blood pressure rising”, we’re using present participles, not gerunds, and that means possessives aren’t appropriate.

In a nutshell

A gerund is a verb form that ends with “-ing” and functions like a noun. When a gerund comes after a noun or pronoun, that noun or pronoun should be in the possessive case: “I appreciate your reading this post”, not “I appreciate you reading this post”.