Good writing is about more than having interesting ideas. It is also about expressing those ideas clearly, accurately, and confidently. Whether you are writing a business email, preparing a college assignment, or posting on social media, small grammar mistakes can distract readers and affect how they view your writing.
The good news is that most common grammar mistakes are easy to correct once you understand the patterns behind them. Many errors happen because certain words sound alike, look similar, or are commonly misused in everyday communication.
This guide explains ten common English grammar mistakes, why they happen, and simple ways to avoid them. Learning Grammar does not require memorizing every rule in a textbook. Instead, it is about recognizing common patterns and developing better writing habits.
1. Your vs. You're
Your and you're are among the most commonly confused words in English because they sound the same when spoken.
Your shows possession:
"Is this your phone?"
You're is a contraction of "you are":
"You're going to enjoy this."
A simple test is to replace the word with "you are." If the sentence still makes sense, use "you're." If it does not, use "your."
For example:
"You're doing a great job."
"You are doing a great job."
"Your writing is improving."
"You are writing is improving." This does not work, so "your" is correct.
2. Its vs. It's
Its and it's create another common problem for writers.
Its indicates possession:
"The company updated its website."
It's is short for "it is" or "it has":
"It's getting late."
To check which form you need, replace "it's" with "it is" or "it has." If the sentence still makes sense, the apostrophe is appropriate.
For example:
"It's been a busy week."
This means:
"It has been a busy week."
However:
"The dog wagged its tail."
Here, "its" shows possession, so no apostrophe is needed.
3. Then vs. Than
Then and than may look similar, but they have different meanings.
Then is generally used for time, order, or sequence:
"We finished dinner and then watched a movie."
Than is used when making comparisons:
"She is taller than her brother."
A useful rule is to associate then with events and sequence, while than is connected with comparisons.
If you are describing what happened next, use "then." If you are comparing two things, use "than."
4. Fewer vs. Less
Fewer and less are often used incorrectly, especially in casual writing.
Fewer is generally used with things that can be counted individually:
fewer students
fewer books
fewer mistakes
fewer cars
Less is generally used with things that are treated as an amount rather than individual items:
less water
less time
less money
less stress
An easy way to remember the difference is this: if you can count something individually, "fewer" is usually appropriate. If you are talking about an amount that cannot normally be counted individually, use "less."
5. Who vs. Whom
Who and whom can seem complicated, but the basic rule is fairly simple.
Who is used as the subject of a sentence:
"Who called you?"
Whom is used as the object:
"Whom did you invite?"
A useful substitution test can help. If you can replace the word with "he" or "she," use "who." If you can replace it with "him" or "her," use "whom."
For example:
"Who sent the email?"
"She sent the email."
But:
"Whom did you contact?"
"I contacted him."
6. Affect vs. Effect
Affect and effect are frequently confused because they look and sound similar.
Affect is most commonly used as a verb meaning to influence:
"The weather affected our travel plans."
Effect is most commonly used as a noun meaning a result:
"The weather had a major effect on our plans."
One helpful memory trick is to think of Affect as Action because both begin with A. Think of Effect as the End result because both begin with E.
There are exceptions to these basic patterns, but this distinction works well in most everyday writing.
7. "Has Underwent" Instead of "Has Undergone"
This mistake is common in professional, academic, medical, and formal writing.
Underwent is the simple past form:
"She underwent surgery last year."
Undergone is the past participle and is used with helping verbs such as has, have, or had:
"She has undergone surgery."
The incorrect form is:
"She has underwent surgery."
The correct form is:
"She has undergone surgery."
A simple rule can help you remember this difference: when "has," "have," or "had" appears before the verb, use "undergone" rather than "underwent."
8. "Could Of" Instead of "Could Have"
The mistake "could of" usually happens because "could've" sounds similar when spoken quickly.
However, the correct written form is always "could have."
Correct:
"I could have helped you."
Incorrect:
"I could of helped you."
The same principle applies to:
could have
should have
would have
When you hear "could've," remember that it is a shortened form of "could have," not "could of."
9. Using Apostrophes to Make Plurals
Apostrophes are often added when writers want to make a word plural, but this is usually incorrect.
Incorrect:
"I bought two apple's."
Correct:
"I bought two apples."
Apostrophes are generally used to show possession or create contractions. They are not normally used to form simple plurals.
For possession:
"The student's notebook is on the desk."
For contractions:
"It is" becomes "it's."
For ordinary plurals:
"Apple" becomes "apples."
"Book" becomes "books."
"Car" becomes "cars."
Keeping these functions separate will help prevent unnecessary apostrophe errors.
10. Subject-Verb Agreement Errors
Subject-verb agreement can become confusing when additional phrases appear between the subject and the verb.
For example:
"The list of items are on the table."
This sentence is incorrect because the main subject is "list," which is singular.
The correct version is:
"The list of items is on the table."
A useful technique is to temporarily ignore phrases that come between the subject and verb. Identify the main subject first, then choose the verb that agrees with it.
For example:
"The collection of old books is valuable."
The subject is "collection," not "books," so the singular verb "is" is correct.
Why These Grammar Mistakes Matter
Making an occasional grammar mistake does not automatically mean that your writing is poor. Everyone makes errors, especially when writing quickly or working under pressure.
However, repeated mistakes can affect how readers perceive your writing. A message filled with recurring grammar problems may appear rushed or careless, even when the information itself is useful and well researched.
This becomes especially important in professional and academic situations. Business emails, reports, applications, essays, and other formal documents often create an impression of your attention to detail.
The good news is that grammar is a skill that can be improved. You do not need to master every rule immediately. Start by identifying the mistakes you make most frequently and focus on correcting those patterns.
How to Build Better Grammar Habits
Understanding grammar rules is useful, but applying them consistently is even more important. A few simple habits can make your writing more accurate.
Read Your Writing Aloud
Reading your work aloud can help you notice awkward sentences, missing words, and certain grammar (https://abnewly.com/underwent/)problems that may be difficult to recognize when reading silently.
Use Substitution Tests
When you are uncertain about a confusing word, try replacing it with a simpler phrase.
For example, replace "you're" with "you are." If the sentence still makes sense, you have probably chosen the correct word.
Track Your Common Mistakes
Most writers have a few recurring problem areas. You might regularly confuse affect and effect, forget apostrophes, or mix up then and than.
Keep a short list of these mistakes and review them when editing your work.
Use Grammar Tools as a Second Check
Grammar-checking software can identify many mistakes, but it should not replace your own understanding of English.
Use these tools as a second layer of proofreading. Learning why a correction is necessary will make it easier to avoid the same mistake in the future.
Final Thoughts
Clear and accurate writing helps readers understand your ideas without unnecessary distractions. Good Grammar does not mean using complicated words or creating long, sophisticated sentences. It means using language correctly and making your message easy to understand.
The ten mistakes discussed in this guide are some of the most common errors in English, but they are also highly manageable. By learning the rules, using simple memory techniques, and paying attention to your personal writing habits, you can gradually eliminate these mistakes.
The goal is not to worry about every sentence you write. Instead, focus on developing habits that make correct grammar a natural part of your writing process. When your grammar becomes more accurate, your ideas can take center stage and make the impression they deserve.