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30 Common Grammar Mistakes to Avoid

Updated on June 20, 2023Grammar

When somebody else finds a grammar mistake in your work, it can be embarrassing. But don’t let it get to you—we all make grammar mistakes.

Common grammar mistakes include punctuation and syntax errors and incorrect word choices. Grammar mistakes often make it difficult for readers to understand a piece of writing; this is why writers should try to avoid them.

The goal is to have polished, clear, mistake-free writing, so we’ll look at some of the most common mistakes so you know how to identify, fix, and avoid them.

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What is a grammar mistake?

A grammar mistake is any incorrect usage of a word or piece of punctuation in writing. In other words, it’s a deviation from established grammatical rules. Grammar rules serve to make writing easier for readers to understand, so when a writer makes one of the common grammar mistakes below, or any other grammar mistake, they risk their work being misunderstood.

However, it’s important to keep in mind that not all deviations from grammatical rules are mistakes. Language is continuously evolving, so a phrase or word choice that’s regularly used today may have been a grammar mistake in the past. And there are instances where breaking grammar rules actually improves your writing. Understanding the most common grammar mistakes, why we make them, and how to correct them can help you navigate evolving language and effective rule-breaking as you develop your writing skills.

30 common grammar mistakes

1 Your vs. you’re

2 Who vs. whom

3 Who’s vs. whose

4 Affect vs. effect

5 Who vs. that

6 That vs. which

7 I.e. vs. e.g.

8 Then vs. than

9 Each and every

10 More than vs. over

11 Less vs. fewer

12 Me vs. I

13 A lot vs. allot vs. alot

14 Farther vs. further

15 Like vs. such as

16 May vs. might

17 Past vs. passed

18 Based off vs. based on

19 Compliment vs. complement

20 Misplaced modifiers

21 Passive voice

22 Possessive nouns

23 Commas

24 Semicolons

25 Title capitalization

26 Apostrophes

27 Punctuation’s place in parentheses

28 Incomplete comparisons

29 Em dash vs. en dash vs. hyphen

30 Subject/verb agreement

30 common grammar mistakes explained

1 Your vs. you’re

Much like to and too, your and you’re are homophones. That means they sound the same when spoken aloud but have two different meanings.

Your is a possessive pronoun. It indicates that something belongs to a singular second person.

You forgot your backpack at school yesterday.

You’re is a contraction of you are.

You’re expected to arrive no later than 6 p.m.

2 Who vs. whom

Who is the subject of a sentence, whereas whom is the object of a sentence.

Who will be hosting the party this weekend?

To whom should I send the package?

3 Who’s vs. whose

Who’s is a contraction of who is. Whose is the possessive form of who, a relative pronoun.

Who’s ready for the exam on Friday?

Whose laptop is this?

4 Affect vs. effect

Affect is a verb that means “to cause an effect.” Effect is a noun that refers to a result.

How will a heat wave affect your vacation plans?

An increased budget will have a major effect on hiring.

5 Who vs. that

Who refers to a person. That refers to an inanimate object. However, that can also refer to a group of people in cases where the group, rather than its members, is emphasized.

My brother is the one who solved the mystery.

I took a course that changed my perspective on climate change.

We’re part of an organization that promotes native plant cultivation.

6 That vs. which

That is used to introduce a clause that adds necessary information to a sentence. Which is used to introduce a clause that adds detail but isn’t critical to the sentence.

One of my dogs, the one that ate a rock, needs to see a vet.

My other dog, which is a terrier, also needs to see the vet.

7 I.e. vs. e.g.

I.e. is short for id est and is used to clarify statements. E.g. is short for exempli gratia and is used to provide examples.

I’ll be late again tomorrow (i.e., my car is still in the shop).

Additionally, a comma should follow these abbreviations, and they should be enclosed in parentheses.

I’ve read lots of novels over the past year (e.g., A Tree Grows in Brooklyn and The Fault in Our Stars).

8 Then vs. than

Then indicates when something will happen. Than is used to compare people or things.

First we’ll go over the homework; then we’ll watch the presentation.

Our cousins are taller than us.

9 Each and every

Each refers to two items. Every refers to three or more items. Additionally, each refers to the individual items in a group, while every refers to the group as a whole.

Each of my children made me a Mother’s Day card.

Every one of my coworkers is going to the dinner.

10 More than vs. over

More than indicates the literal quantity of things being discussed. Over can indicate an object’s physical position or a figurative amount larger than another mentioned in the same sentence.

She owns more than ten jackets.

We’re going to come in over our budget.

11 Less vs. fewer

Less is used to describe an abstract or otherwise uncountable amount of items. Fewer is used for countable numbers of items.

The students had less time to work on the assignment today.

If fewer people used disposable water bottles, there would be less plastic in landfills.

12 Me vs. I

I and me are both first-person singular pronouns. Use I when you’re the subject of the sentence and me when you’re the object of the sentence.

It was almost midnight, so I didn’t stop to pick up my shoe.

You want me to dance with you?

13 A lot vs. allot vs. alot

A lot can be a pronoun or an adverb. It means “often” or “a large amount.” Allot is a verb that means “to distribute.” Alot is not a word. Avoid it in your writing.

There were a lot of jellyfish.

We were allotted two notebooks and five pens each.

14 Farther vs. further

Farther refers to literal distance. Further means “more.”

The island looked farther away than ever.

We want no further communication with your company.

15 Like vs. such as

Like is used to make a comparison, while such as is used to provide specific examples.

The couch has black and white spots like a dalmatian.

We have many pizza toppings, such as peppers, pineapple, and pepperoni.

16 May vs. might

Generally, may is used in the present tense to ask for permission and to indicate something that is likely to happen. Might is used with the past tense and to describe things that are either unlikely or didn’t happen.

May I bring a guest to the book signing?

There might have been time for discussion, but the fire alarm went off.

17 Past vs. passed

Past refers to something that has already happened. It can be a noun, an adjective, a preposition, or an adverb. Passed is a verb.

Our grandfather told us stories about the past.

The SUV passed on our right.

18 Based off vs. based on

This is an example of language evolving, and perhaps one day, based off will be considered grammatically correct. But currently, based on is considered to be the correct phrasing. Both of these phrases are used to indicate the facts or circumstances that drove a specific decision or conclusion.

Based on the rain in the forecast, I decided not to water my garden today.

Another version of this phrase, based off of, is never correct.

19 Compliment vs. complement

A compliment is a kind word or bit of praise for another person or thing. To complement someone or something means to enhance their skills or assets with other skills or assets.

I liked Dara’s presentation, so I paid her a compliment.

Dara’s background in UX design complements my front-end development experience.

20 Misplaced modifiers

A misplaced modifier is a word or phrase that’s too far away from the noun it’s modifying. A misplaced modifier can make a sentence confusing for readers. Here is an example of a sentence with a misplaced modifier, which is bolded:

My sister adopted another cat named Ghost.

So she has two cats named Ghost now?

Here is a corrected version of this sentence:

My sister adopted another cat and named her Ghost.

21 Passive voice

The passive voice isn’t inherently incorrect, but many writers use it when the active voice would be a more accurate, clearer choice.

Passive voice: Breakfast was prepared by me.

Active voice: I prepared breakfast.

22 Possessive nouns

Possessive nouns are versions of nouns that show ownership. Often, they use apostrophes.

For a singular possessive noun, the apostrophe goes before the s.

Maryam’s notebook.

For a plural possessive noun, the apostrophe goes after the s.

The students’ grades.

That said, there are different schools of thought about what to do when a singular possessive noun ends in the letter s. Some say the apostrophe goes at the end, without adding an s.

That’s James’ car.

Chicago style stipulates that when a name ending in s becomes possessive, you add an apostrophe and an s.

That’s James’s car.

23 Commas

Commas are versatile punctuation marks, so it’s easy to use them incorrectly. Commas are used to create short pauses within sentences, such as to separate items in a list, distinguish independent clauses, or note appositives.

I went to the store for butter, flour, and milk.

I went to the store for butter flour and milk.

24 Semicolons

Semicolons are most frequently used to separate independent clauses within a sentence. They’re also used to separate items in a serial list when those items contain punctuation of their own.

Amalia is taking twenty credits this semester; her goal is to graduate early.

I need the weather statistics for the following cities: London, England; Paris, France; and Perth, Scotland.

25 Title capitalization

Although it can vary between style guides, the general rules for title capitalization are:

  • Articles are lowercase unless they’re the first or last word of the title
  • Nouns, verbs, adjectives, and adverbs are always capitalized

The Cat in the Hat

Things Fall Apart

26 Apostrophes

Apostrophes create a few types of words:

  • Contractions (she did = she’d)
  • Singular possessive nouns (Jason’s)
  • Shortened colloquial words (it was = ’twas)

In some cases, they also create plurals.

Remember to dot your is.

Remember to dot your i’s.

27 Punctuation’s place in parentheses

When it comes to parentheses and other punctuation, there are a couple of rules to follow.

  • If the text in parentheses is a complete sentence and is separate from surrounding sentences, the period goes inside the parentheses.
  • Additionally, a phrase that could stand alone as a complete sentence can also be contained inside another complete sentence.

My house has blue trim. (My neighbor’s house has blue trim, too.)

My house has blue trim (my neighbor’s house has blue trim, too).

My house has blue trim (with white windows) and a green door.

Question marks and exclamation marks are the exceptions to the rule. When they’re part of a parenthetical passage enclosed in another sentence, they always go inside the parentheses, whether it’s a complete sentence or a fragment.

Dimo got lost on the way to his interview (but he wasn’t late so they never knew!).

  • Use commas after parentheses, not before.

Because parenthetical text usually relates to what’s directly before it, it shouldn’t follow a comma. However, it’s completely normal to place a comma after parentheses, without a space.

The party was too quiet, (the DJ canceled) so Gina brought out her guitar.

The party was too quiet (the DJ canceled), so Gina brought out her guitar.

28 Incomplete comparisons

When you make a comparison in your writing, you need to mention both (or all) of the things you’re comparing.

My car is faster than my cousin’s car.

An incomplete comparison is a comparison that fails to mention one or more of the things being compared.

My car is faster.

29 Em dash vs. en dash vs. hyphen

Em dashes, en dashes, and hyphens are frequently mixed up. Here is a quick look at them:

Em dash: —

En dash: –

Hyphen: –

Use an em dash when another type of punctuation, like parentheses or a pair of commas, doesn’t quite capture the tone you need. Em dashes have a quick, casual connotation, so they’re often used to indicate an aside or sudden tone change in a sentence.

They are afraid of two thingsspiders and senior prom.

En dashes are used to show date and time ranges. They can also be used to link complex compound adjectives when both halves are hyphenated or when one of the parts is a multi-word noun or an open compound adjective.

We’re open MondaySaturday.

The Nobel Prizewinning author will be reading from her book at the library tonight.

Hyphens are used to connect words. Often, this is to create a compound modifier, which is a multi-word adjective.

Antonio LuisRodríguez just finished writing his most attentiongrabbing novel yet.

30 Subject/verb agreement

In any sentence, the subject and verb need to be in the same tense.

My classmates hopes our teacher will be back soon.

My classmates hope our teacher will be back soon.

Avoid common grammar mistakes with Grammarly

All of the rules, tricks, and tips for using grammar correctly can be a lot to remember, and Grammarly can help. Grammarly checks your writing for common spelling, grammar, and punctuation mistakes. And now, with Grammarly’s generative AI assistance, you can get support with all stages of the writing process: ideation, composition, revision, and comprehension. Grammarly’s generative AI features are available when you download Grammarly

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