1. The classic your/you’re mistake.
“Your” - it belongs to you. “You’re” - you are. Simple as that.
2. When subjects and verbs don’t agree.
There are towels in the closet. “Towels” are a plural object, so “are” is the appropriate form of the verb in this sentence.
3. Whenever someone splits infinitives.
The infinitive form of a verb is the form it takes when it doesn’t apply to any specific subject - “to focus,” for example. By placing the adverb “really” in between the words “to” and “focus,” it splits the infinitive. Keep it together - the infinitive and yourself.
4. Failing to use the subjunctive.
If I were you, I’d check out this primer on how to use the subjunctive.
5. Trying to connect two sentences with a comma, AKA comma splicing.
Two independent clauses can’t be connected by a comma. They just can’t. You can put a period after the first one and start a new sentence, you can use a semicolon, or you can use a hyphen. Just no comma splices.
6. When someone puts punctuation outside of a quotation mark.
Punctuation goes inside the quotation mark. Just do it.
7. Mixing up “who’s” and “whose.”
Although the apostrophe usually signifies ownership, in this case, “who’s” actually stands for “who is.” If you want to talk about who owns something, the correct word is “whose.”
8. Using “lay” when you really mean “lie,” or vice versa.
“Lay” is only used when you are acting upon an object other than yourself. So if it’s time for you to get in bed, you are going to “lie” down because you are doing something to yourself.
9. The “it’s” versus “its” conundrum.
Just like with “who’s” and “whose,” this is another time when the apostrophe means something other than ownership. In this case, “it’s” is a contraction meaning “it is.”
10. When someone uses a double negative.
If you didn’t do nothing, then you did do something. “Didn’t” and “nothing” are both negative, so they essentially cancel each other out and make this sentence mean the exact opposite of what the speaker intended.
11. Not knowing the difference between “who” and “whom.”
“Who” is the subject of the verb,” while “whom” is the object. “You saw who?” is incorrect because “who” is not acting, but being acted upon. “Who” is the object, not the subject. Who’d have thought it could be so easy?
12. Saying “they” to refer to a singular object.
“They” is plural, so unless you’re talking about more than one person, you need to say “he” or “she.”
13. Leaving participles dangling.
The cars are not walking along, which is what this sentence currently implies. The participle “walking along” is dangling all by its lonesome with no subject to attach itself to.
14. When “less than” and “fewer than” are mixed up.
“Fewer” is used in reference to people or things in their plural form. “People” is the plural form of “person,” so this sentence needs to be changed to “fewer than.”
15. Using “I” when you really mean “me.”
“I” is a subject. “Me” is an object. Use them wisely.