Me vs. I
This is one rule you probably heard starting back in primary school. If you uttered, “Me and Mike went to the store,” you probably heard someone admonish, “Mike and I!” The problem with that, though, is that many people end up over-correcting. Though “Mike and I went to the store” is right, in some sentences, it is correct to use “me” – it depends on whether the first-person pronoun is a subject or an object. Here’s an easy way to know: Take out the other person, and see if “me” or “I” makes sense. “Me went to the store” is incorrect, but “My mother met me at the store” is perfectly fine. So it’s grammatically correct to say “My mother met me and my dad at the store,” not “my dad and I.”
its vs. it's
Use the wrong form of “its,” “there,” or “your,” and you’re (a contraction of “you are”) sure to have the grammar police wag their (the possessive form of “they”) fingers at you. But we do have to admit, when it comes to “it’s” vs. “its,” the confusion is easy to understand. In virtually every other situation, an apostrophe indicates possession. Bob’s car. Lisa’s house. Reader’s Digest. But when it comes to “it,” the possessive form is the form without the apostrophe. “The rabbit crawled into its burrow” is the correct use. In the case of “it’s,” the apostrophe means the word is a contraction of “it is.” It serves the same function as the apostrophe in “won’t” or “shouldn’t.”
Who vs. whom
Boiled down, this rule is simple. “Who” refers to the subject of a sentence or clause, while “whom” refers to the object. But when you actually get down to using the two words in a sentence, that’s when things get dicey. You would ask, “Who went shopping with you?” since “Who” is the subject. But you could also ask, “With whom did you go shopping?” since “You” is the subject. Grammarly recommends a tip that should help you figure it out, if you’re truly determined to. Substitute the “who/whom” pronoun with “he/him” or “she/her,” rearranging the sentence if necessary. “She went shopping with you” (“who”), but “You went shopping with her” (“whom”).