13 Common Grammar Mistakes to Avoid in Writing

by Rahimah Sultan

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It can be embarrassing when somebody else finds a grammar mistake in your work, but don’t let it get to you. We all make grammar mistakes.


What is a grammar mistake?


A grammar mistake is any incorrect usage of a word or a deviation from established grammatical rules.

As language continually evolves, a phrase or word choice that’s used today may have been a grammar mistake in the past.

We’ll view 13 common grammar mistakes to avoid in writing so you’ll know how to identify, fix, and steer clear of them.

Your goal is to have clear, polished, mistake-free writing. So, we’ll look at 13 common grammar mistakes and show you how to fix them.


1.   Who vs. that


Use who when referring to a person. That is used for inanimate objects.

Example          My brother is the one who wrote the book.

Example          I bought a purse that is light to carry.

Example          They’re part of an organization that promotes organic farming.


2.   Affect vs. effect

Affect is a verb that means to cause something to happen. Effect is a noun that indicates a result.

Example          How will the continuous rain affect construction?

Example          The increasing layoffs will have a major effect on the economy.


3.   Who’s vs. whose

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

Example          Who’s ready to go?

Example          Whose bookbag is this?

4.   Who vs. whom

Who is the subject in a sentence, while whom is the object.

Example          Who will be going to the banquet this weekend?

Example          To whom shall I address the package?


5.   Less vs. fewer

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

Example          The students had less time to practice today.

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


6.   I.e. vs. e.g.

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

Example          I’ll be off again tomorrow, (i.e., I’m still very sick).

Example          I’ve read lots of books over the past year (e.g., Undaunted, A Tree Grows in Brooklyn, and How Green was my Valley).

Always add a comma following these abbreviations, and enclose them in parentheses.


7.   Then vs. than

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

Example          First we’ll have lunch; then go to a movie.

Example          All my brothers are taller than me.


8.   Each and every

Each refers to two items or the individual items in a group. Every refers to three or more items or to the group as a whole.

Example          Each of my children came to visit me this year.

Example          Every one of my coworkers is going to the restaurant.


9.   May vs. might

May is generally 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 either didn’t happen or are unlikely to happen.

Example          May I bring a guest to the party?

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


10. Farther vs. further

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

The mountain looked farther away than ever.

We’ll have no further communication.


11. Past vs. passed

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

Example          My cousin told us stories about the past.

Example          The bus passed on our right side.


12. Passive voice

While not inherently incorrect, many writers use the passive voice when the active voice would be a more correct, clearer choice.

Passive voice: The layout was prepared by me.

Active voice: I prepared the layout.


13. Possessive nouns

Possessive nouns are versions of nouns that show ownership. They often use apostrophes.

Example          That’s John’s letter opener.


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

Example          The marchers’ instruments.

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.

Example          That’s Jonas’ car.

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

Example          That’s Jonas’s car.


These are just 13 common grammar mistakes to avoid in writing, but there are many others that people make. Practice, reading extensively, and using grammar-checking tools will help you spot mistakes and make corrections. With time, practice, and patience, you’ll be able to improve your grammar skills and become a more confident writer.

I recommend Grammarly as a checking tool. It’s free.


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