Common Grammar Mistakes Cheat Sheet

Misused Word(s)	Rule	Examples
Who/Whom	“Who” is subjective and is used when the pronoun acts as the object of a clause. Usage depends on whether you are referring to the subject or object of a sentence. To test, substitute “he” or “she” for “who,” and substitute “him” or “her” for whom.	Who loves you? (She loves me.) I consulted with a doctor whom I met in school. (I consulted with him.)
Which/That	“That” is a restrictive pronoun, which means the phrase following it is needed to understand the preceding statement. “Which” introduces a relative clause and is used when there are qualifiers that may not be essential.	I don’t like buying clothes that aren’t made in the USA. You should only buy clothes made locally, which are usually sold at smaller local businesses.
Lay/Lie	“Lay” requires a direct object (past tense: “laid”). “Lie” doesn’t need an object (past tense: “lay”). Common mistake: People use the past tense of “lay” when they mean to use the past tense of “lie.”	I lay my head upon the pillow. Last night, I laid my head upon the pillow. The stones lie near the river. The stones lay near the river, waiting to be washed.
Nor/Or	“Nor” means “and not.” Rule of thumb: Use “nor” with “neither” and “or” with “either”.	I bet neither Mike nor Jessie will like the movie. I bet either Mike or Jessie will not like the movie.
Affect/Effect	“Affect” is a verb that means “to influence or produce an impression.” “Effect” is a noun that means “the result of.”	That movie affected me like no other movie has. I felt no effect from the movie, I wish it affected me, but I thought it was boring.
Since/Because	“Since” refers to time. “Because” refers to causation.	Since I saw you last, I’ve gotten a new job. Because I saw you, I looked into that new job you recommended.
Fewer/Less	“Few” and “fewer” are for things you can count. “Less” is for hypothetical quantities.	I ate fewer calories today than I did yesterday. I need to eat less food so I can lose weight.
Whether/If	“Whether” expresses a condition where there are two or more alternatives. “If” expresses a condition where there are no alternatives.	I don’t know whether I will meet up with you later. I will meet up with you tonight if I finish my homework.
May/Might	Both suggest there is a possibility of something happening, but use “may” when there’s a greater likelihood and “might” when there’s little to no chance.	I may see you later if I can finish my essay. I might go to Europe this summer—if I can get over my fear of flying.
That/Who	Whenever you write about people, use “who” to refer to them.	Jane is the girl who lives above me.
Than/Then	“Than” is used when comparing things. “Then” is used when referring to time.	She is much taller than me. I will see you first and then go to the store.
It’s/Its	“It’s” is a contraction of “it is.” “Its” is a possessive pronoun or adjective.	It’s going to rain tomorrow. The dog licked its paw.
There/Their/They’re	“Their” is used when referring to ownership or possession. “They’re” is a contraction of “they are.” “There” is used when referring to location.	Their dog was barking so loudly, I couldn’t sleep. They’re going to go the movies later. There is that sock I was looking for.
Complement/ Compliment	“Complement” refers to something that adds to or completes something else. “Compliment” is something nice said about you.	The fresh herbs really complement the chicken. She complimented me and said she liked my shoes.
Loose/Lose	“Loose” refers to when something is coming undone. “Lose” is the opposite of “win” or “gain.”	My pants are so loose, I need a belt to keep them up. If I lose more weight, I’ll need a belt to keep my pants up.