So, normally, whenever I hear a friend say something like “My parents invited Tom and I,” my best judgment tells me to keep my yap shut. But when a friend said that last week, I found myself in an awkward position.
For one thing, this friend is much better educated and much better read than I. But that's not what caused my inner turmoil. The conflict arose from the fact that I'm teaching this friend copy editing.
Oh, and here's another complicating factor: My little policy about not correcting people's grammar — well, I don't follow it as much as I should. In recent years, long before my friend asked to learn copy editing, I had already told her several times that it's more grammatical in that context to say “Tom and me,” not “Tom and I.”
Here's why: Contrary to a popular perception that “and I” is always better than “and me,” it actually depends on how it's used. Whenever the compound is the subject of a clause, then you want I. For example: Tom and I enjoy pizza. In this sentence, the Tom and I are performing the action: enjoying. So this compound is the subject.
But in my friend's sentence, which began “my parents invited,” the parents are the subject of the verb. The object is what comes next: “Tom and me.”
The concept of subjects and objects are much easier than they sound. If you know instinctively that “Me went to the movies” and “Kiss I, you fool” are wrong, then you already get the concept. I, you, he, she, we, it and they are subject pronouns. Me, you, him, her, us, it and them are object pronouns.