20 Common Grammar Mistakes and How to Avoid Them

If you are a grammar nerd like me, you see common grammar mistakes all the time. Everywhere you look, particularly online, they just jump out at you and make you want to chew off your fingernails. But even if you’re not a grammar nerd, it’s important to recognize and avoid these 20 common grammar mistakes so that your writing is as professional as possible. After all, a few mistakes in grammar could just ruin a resume or other professional paper.

So let’s look at 20 common grammar mistakes to avoid. This is a quick and dirty overview – so use it as a reference. If you need further review of these common grammar mistakes, feel free to refer to our more in-depth blogs for a greater explanation.

1. To or Too

To is the most common usage. It is usually used in front of a noun or a verb and means a direction, recipient, or action such as to go to something.

Too means “also” as in: Let me go too!

You really don’t want to mix these two up, particularly in your professional writing. It is a fairly obvious difference, and using one of these common grammar mistakes just screams that you have lapses in your education – or you lack attention to detail.

2. Affect or Effect

I know they sound alike, but these words are very different. The difference here is not so obvious as in #1, and confuses so many people that writers have taken to using the word “impact” as a replacement – just to avoid using the wrong word. But let’s see if I can help you understand one of these common grammar mistakes.

Affect is a verb. This is the big distinction in a nutshell. It is used to show action.

    They didn’t know how the rainfall would affect the crops.

Effect is a noun. It is used as a subject or object. It is also used in everyday language far less than its homonym affect.

    The effect of the rainfall was yet to be seen.

For more about these two words, read our post on the difference between affect vs. effect.

3. Who or Whom

This one is a little tougher because it involves knowing if you need a subjective pronoun or an objective pronoun. Here’s a quick refresher: subjective pronouns are the subject of a sentence, while objective pronouns are direct objects and objects of the preposition.

Who is the subjective case.

    Who decided to come to the show?

Whom is used in the objective case.

    The show was attended by whom?

You can learn more in our article, The Difference Between Who vs. Whom.

4. Misplaced Modifiers

Modifiers are words or phrases that give us more information about other words and phrases within a sentence. The modifier should always appear close to what it is modifying. A misplaced modifier could produce some embarrassing and confusing results.

    They walked into the tavern and ordered a drink that was dirty and filled with cockroaches.

Yikes! However, what the author meant to say was that the tavern was dirty and filled with cockroaches, not the drink.

    They walked into the tavern that was dirty and filled with cockroaches and ordered a drink.

5. Possessive Apostrophe

If a noun is possessive, you will need to add an apostrophe to show that it’s possessive. However, there are rules regarding where to put that pesky apostrophe.

If the noun is singular and does not end in the letter “s,” add an apostrophe and then the letter “s.”

    The bull’s head was massive.

If the noun is plural OR ends in an “s,” put the apostrophe after the letter “s” and don’t add another “s.”

    The girls’ banner was flying high that day.

    The bus’ driver was asleep at the wheel.

6. Its or It’s

Its is a possessive.

    The bug didn’t know its strength.

It’s is a contraction of it is.

    It’s beginning to look like rain.

7. Your or You’re

Your is a possessive.

    You shouldn’t have washed your car.

You’re is a contraction of you are.

    You’re looking very happy today.

8. Their or They’re or There

Their is a possessive meaning “owned by a group.”

    You should have seen their parade float!

They’re is a contraction of they are.

    They’re happy that you liked the parade.

There is a location.

    Put the trophy over there.

9. Dangling Participle

A participle has many jobs but one of them is to be used as an adjective. A dangling participle has no subject to describe! Therefore, it dangles. This leads to a lot of confusion for the reader.

    With the huge lump on his head, the bird attacked Johnny.

Who had the lump, the bird or Johnny?

10. Peek or Peak or Pique

Peek is to look.

    We took a peek in that direction.

Peak is the top of something that comes to a point.

    We climbed to the mountain’s peak.

Pique is to stimulate interest or curiosity.

    The movie served to pique our interest.

11. That vs. Who

Use that when you are describing an object.

    It’s always my car that blows a gasket.

Use who when you are describing a person

    It’s always Amy who blows a gasket.

12. Alot

Bad news – alot is not a word! If you are writing about a whole bunch of something you use the two words a lot.

    There was a lot of ham on that sandwich.

Be careful not to use the word allot, which means “to set aside.”

    They decided to allot $50 for the hamster funeral.

13. Loose or Lose

These get mixed up because they are spelled almost the same.

Loose means something is not tight.

Lose means to not be able to find.

    You may lose that nut if it comes loose from the bolt.

14. Ensure or Insure or Assure

Ensure means to make something certain.

Insure means to provide insurance for.

Assure means to promise something in confidence.

    Let me assure you that I will ensure the real estate agent has this house insured.

15. Less or Fewer

Ever wonder which to use? Here’s how you remember:

You use fewer when something is countable.

You use less when something is not countable.

    I’m going to ingest fewer calories because I want to exercise less.

16. No Commas In a Compound Sentence

If you have two independent clauses in a sentence, they need to be separated by a comma.

    He drove the truck like a madman, and the truck strained under the speed.

17. Semicolons

Speaking of compound sentences, a semicolon can also be used to separate two independent clauses. This is a stylistic choice. However, keep in mind that many people overuse semicolons, which in today’s culture can be a bit irritating.

People want you to cut to the chase, not regale them with your impressive command of grammar. The fact is that a simple comma will usually do the trick, and people who overuse semicolons can appear to be “overeducated” or snooty. Additionally, a bunch of semicolons can make a piece of writing seem cluttered. Today’s audience wants streamlined and readable writing instead.

    He drove the truck like a madman; the truck strained under the speed.

18. Then or Than

Then shows an action that has a place in time.

    Ralph arrived at the move, then he got popcorn.

Than is used to show a comparison.

    Ralph decided he would rather go to the movie than the golf course.

19. Among or Between

You use between when you are talking about two or more things that can be clearly separated.

    I hate to choose between carrots and broccoli.

You use among when the items are in a group.

    She is among the brightest in her class.

20. Should of, Would of, Could of

You never include the word of behind should, would, or could. You always use the word have instead.

    We would have walked away if we could have seen the exit.

Hopefully, these quick and dirty tips will help you out for your next writing assignment! What are some other common grammar mistakes that trip you up? Let us know in the comments.

P.S. Become a better writer. Find out more here.


  • Dawne DuCarpe

    Dawne received a Double Bachelor of Arts Degree from the State University of New York at Buffalo. After having three children and raising them at home for a decade, she went to law school and graduated Cum Laude in 2007. After years of criminal law practice, she stepped back to homeschool her boys through High School. When she is not schooling her kids, writing novels on the criminal justice system, or writing for Magoosh, she enjoys spending as much time as she can with her husband and kids having fun!

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