Even the most seasoned writers slip up on grammar from time to time. Whether it's a misplaced comma, an unclear pronoun, or mixing up "their" and "they're," small mistakes can cloud your message and weaken your writing. In this article, we’ll identify some common grammar mistakes, outline what to look for, and show you how to fix them with clear examples.
1. Run-On Sentences
A run-on sentence (also called a fused sentence) occurs when two independent clauses — each of which could stand as a complete sentence — are joined without proper punctuation or connecting words.
This can often be corrected by adding a coordinating or subordinating conjunction, or by separating the clauses with a period or semicolon.
Examples:
The next step will be tough, you should get ready as soon as you can. (Incorrect)
The next step will be tough, so you should get ready as soon as you can. (Correct)
The next step will be tough. You should get ready as soon as you can. (Also correct)
I can’t figure out how to set up this rice cooker, it came without an instruction manual. (Incorrect)
I can’t figure out how to set up this rice cooker because it came without an instruction manual. (Correct)
I can’t figure out how to set up this rice cooker; it came without an instruction manual (Also correct)
2. Comma Splice
A comma splice is a specific type of run-on sentence that occurs when two independent clauses (complete sentences) are incorrectly joined with just a comma, without a coordinating conjunction (like and, but, or so). A comma alone isn't strong enough to connect two complete thoughts.
Remember: All comma splices are run-on sentences, but not all run-ons are comma splices. Think of comma splices as a specific type of run-on where a comma is used instead of something stronger.
Examples:
She enjoys painting, she takes classes every weekend. (Incorrect)
She enjoys painting. She takes classes every weekend. (Correct)
She enjoys painting, and she takes classes every weekend. (Correct)
She enjoys painting; she takes classes every weekend. (Correct)
My friends and I like to go skiing, we have so much fun together on the weekends in winter. (Incorrect)
My friends and I like to go skiing. We have so much fun together on the weekends in winter. (Correct)
My friends and I like to go skiing; we have so much fun together on the weekends in winter. (Correct)
He planned to study for the exam, however he ended up going to the party instead. (Incorrect)
He planned to study for the exam. However, he ended up going to the party instead. (Correct)
He planned to study for the exam; however, he ended up going to the party instead. (Correct)
You can fix a comma splice by:
Replacing the comma with a period
Using a semicolon
Or adding a coordinating conjunction (and, but, so, etc.) after the comma
3. Sentence fragments
A sentence fragment is an incomplete sentence. It might look like a full sentence—with a capital letter and a period—but it’s missing an essential element. For a sentence to be complete, it must contain at least one independent clause, which requires:
A subject (someone or something doing the action)
A predicate (usually a verb that expresses an action or state of being)
A complete thought (the sentence must make sense on its own)
Fragments often occur when a dependent clause is left standing alone, or when a phrase lacks a subject or verb.
Examples:
Looking forward to meeting you next Sunday. (Incorrect)
(Who’s looking forward to it?)
I’m looking forward to meeting you next Sunday. (Correct)
Although the weather was perfect. (Incorrect)
(What happened as a result?)
Although the weather was perfect, the event was canceled. (Correct)
I found a great new position in tech. The remedy for all my financial problems. (Incorrect)
I found a great new position in tech, which will be the remedy for all my financial problems. (Correct)
4. Subject-verb agreement:
Basic Rule
The verb must agree with the subject of the sentence
Singular subject → singular verb
Plural subject → plural verb
Examples:
She walk to school every day. (incorrect)
She walks to school every day. (correct)
They walks to school every day. (incorrect)
They walk to school every day. (correct)
Compound subjects
If two or more subjects are joined by "and," they usually take a plural verb.
My brother and sister lives in Toronto. (incorrect)
My brother and sister live in Toronto. (correct)
Jane Moore, Mike Smith, and John Green is being promoted. (Incorrect)
Jane Moore, Mike Smith, and John Green are being promoted. (Correct)
But if the compound subject refers to one entity, use a singular verb.
Rice and beans are a popular dish in many cuisines. (Incorrect)
Rice and beans is a popular dish in many cuisines. (Correct)
(Rice and beans is considered one combined dish.)
Collective Nouns
A collective noun (e.g., team, family, group) can take either a singular or plural verb depending on whether the group is acting as a unit or as individuals.
Barnes & Noble are hosting a special event for local authors. (Incorrect)
Barnes & Noble is hosting a special event for local authors. (Correct)
(Barnes & Noble is a company and therefore a single unit.)
The staff is preparing their own presentations. (Incorrect)
The staff are preparing their own presentations. (Correct)
(Each staff member is working individually.)
The staff is preparing a presentation. (Correct)
(The staff is working as a single, collective unit.)
Indefinite Pronouns
Some pronouns are always singular, others always plural, and a few can be either, depending on context.
Always singular: everyone, someone, nobody, each, either
Everyone is late. (Correct)
Everyone are late. (Incorrect)
Always plural: few, many, both, several
Several of my friends are parents. (Correct)
Several of my friends is parents. (Incorrect)
Can be either: all, some, none
All of the cake is gone. (Correct)
All of the cookies are gone. (Correct)
5. Passive vs. Active voice
In the active voice, the subject of a sentence is performing an action. In the passive voice, the subject receives an action instead of doing it.
The active voice is usually more direct, vigorous, and generally preferred in most writing.
Examples:
Active: The manager approved the new policy.
Passive: The new policy was approved by the manager.
Active: The wind carried their voices across the field.
Passive: Their voices were carried across the field by the wind.
Active: Dead leaves covered the ground
Passive: There were a lot of dead leaves lying on the ground.
While the active voice is usually clearer and more direct, the passive voice is sometimes preferred. Here are some situations where you could use the passive voice:
If the actor is unknown or unimportant:
The jewels were stolen from the high-security vault last night.
(We don’t know who stole the jewels.)
If the action matters more than the actor:
The law was passed after years of public pressure.
(The emphasis is on the fact that the law passed, not on who passed it.)
If trying to sound more formal or objective (especially in academic or scientific writing):
The data was analyzed according to rigorous scientific standards.
(This keeps the focus on how the data was handled, not who did it, which is important in a scientific paper.)
For stylistic reasons (poetry, narrative, suspense):
His name was never spoken again.
(This adds mystery and weight by focusing on the consequence, not the actor.)
6. Misplaced or dangling modifiers
Misplaced or dangling modifiers occur when an adjective, phrase, or clause is placed too far from the word it is supposed to modify, making the meaning unclear or confusing.
Examples:
On my way to work, I noticed a blue woman’s handbag in the gutter. (Incorrect)
It's unclear if the handbag belongs to a blue woman or if the handbag is blue. The modifier (blue) needs to be moved next to the word it is modifying (handbag).
On my way to work, I noticed a woman’s blue handbag in the gutter. (Correct)
My new girlfriend ordered an expensive plate of lobster at the restaurant last night. (Incorrect)
It's unclear whether the plate or the lobster was expensive.
My new girlfriend ordered a plate of expensive lobster at the restaurant last night. (Correct)
While walking down the street, the car almost hit me. (Incorrect)
The modifier "while walking down the street" dangles because it implies the car was walking down the street. The sentence doesn’t clearly state who was walking.
Correct: The car almost hit me while I was walking down the street.
7. Unclear pronoun reference / unclear antecedent
A pronoun refers to a specific noun (called the antecedent) mentioned earlier in a sentence or paragraph. When the antecedent is unclear or ambiguous, it becomes difficult for the reader to know what or whom the pronoun is referring to.
Whenever you use pronouns like he, she, they, it, or this, make sure it's obvious to the reader who or what you're referring to. To avoid confusion, make sure:
There's only one possible antecedent.
The pronoun appears close to its antecedent.
Examples:
When Brad started arguing with Claude, he went red in the face. (Unclear)
It's unclear whether Brad or Claude went red in the face.
When Brad started arguing with Claude, Brad went red in the face. (Clear)
Brad went red in the face when he was arguing with Claude. (Clear)
When Sarah finally met her long-lost sister, she was crying in a subway station. (Unclear)
It’s unclear whether Sarah or her sister was crying.
Sarah was crying in a subway station when she finally met her long-lost sister. (Clear)
8. Parallel Structure Errors
Parallel structure errors occur when elements of a sentence that are similar in meaning or function are not expressed in a grammatically consistent way. These errors often happen in lists or with paired ideas connected by conjunctions like and, or, and but.
Maintaining parallel structure means using the same grammatical form for all elements in a series or comparison.
Examples:
I have been thinking about signing up to study phonetics, literary devices, and an English teacher. (Incorrect)
I have been thinking about signing up to study phonetics, literary devices, and English teaching. (Correct)
(Each item in the list should be a field of study, not a person.)
I really need to concentrate on grammar, spelling, and my punctuation. (Incorrect)
I really need to concentrate on grammar, spelling, and punctuation. (Correct)
I really need to concentrate on my grammar, spelling, and punctuation. (Correct)
(All items are nouns, or possessive noun + noun.)
You can choose to attend the workshop in person or the virtual option. (Incorrect)
("to attend" is a verb phrase, "the virtual option" is a noun phrase — not parallel.)
You can choose to attend the workshop in person or virtually. (Correct)
(Both are verb phrases: “to attend in person,” “to attend virtually.”)
9. Tense Agreement
Tense agreement means using the same verb tense consistently within a sentence or related group of sentences, unless a shift in time clearly justifies a change.
Changing tense unnecessarily within a sentence is a common error that can confuse readers.
Examples:
He starts the car and then accelerated away in a cloud of tire smoke. (Incorrect)
(Mixes present tense "starts" with past tense "accelerated")
He started the car and then accelerated away in a cloud of tire smoke. (Correct)
(All past tense.)
She was walking to the store when she hears a loud noise. (Incorrect)
(Mixes the past continuous tense with the present tense.)
She was walking to the store when she heard a loud noise. (Correct)
(Both actions in past tense.)
She walks to the store when she hears a loud noise. (Correct)
(Both actions are in the present tense.)
10. No comma after an introductory element
A comma is typically used after introductory words, phrases, or clauses that come before the main clause in a sentence. These introductory elements set up the main idea, and the comma helps to separate them for clarity.
Examples:
Just in case you are worried I’ll be home by twelve. (Incorrect)
Just in case you are worried, I’ll be home by twelve. (Correct)
(The introductory phrase "Just in case you are worried" needs a comma before the main clause.)
Therefore I shall wait until I am called. (Incorrect)
Therefore, I shall wait until I am called. (Correct)
(The word "Therefore" is an introductory element, so a comma follows it.)
Determined to make their flight on time they rose at dawn. (Incorrect)
Determined to make their flight on time, they rose at dawn. (Correct)
(The phrase "Determined to make their flight on time" acts as an introductory clause, and the comma separates it from the main clause.)
11. Unnecessary and redundant commas
Commas should not be added arbitrarily or based on where you feel a pause is needed. Instead, commas serve specific purposes, and misplacing them can cause confusion or disrupt the flow of the sentence. One common mistake is placing commas around essential or restrictive information, or before conjunctions such as "because," "and," "as well as," or "or."
Examples:
I rarely go to the city centre, because I hate the crowds. (Incorrect)
I rarely go to the city centre because I hate the crowds. (Correct)
(The clause "because I hate the crowds" is essential to the meaning, so no comma is needed.)
He says he wants to start a new course in writing, or literature. (Incorrect)
He says he wants to start a new course in writing or literature. (Correct)
("Or literature" is part of the same thought and doesn’t need a comma.)
Many children, of working parents, walk home from school by themselves. (Incorrect)
Many children of working parents walk home from school by themselves (Correct)
(The phrase "of working parents" is essential to the meaning of the sentence and should not be separated by commas.)
12. Missing Comma with Nonrestrictive Element
Just as you should not put commas around essential or restrictive information in a sentence, you must remember to put commas around information that is nonessential or nonrestrictive.
If the information is not essential to the meaning of the sentence, you need to be sure to set it off with commas. Here are examples of sentences without proper commas around the nonrestrictive element:
The conference which was scheduled for next week has been postponed. (Incorrect)
The conference, which was scheduled for next week, has been postponed. (Correct)
(The clause "which was scheduled for next week" is non-restrictive, so it should be set off by commas.)
My brother who lives in New York is visiting us this weekend. (Incorrect)
My brother, who lives in New York, is visiting us this weekend. (Correct)
(The clause "who lives in New York" is non-restrictive, so it should be set off by commas.)
13. The Oxford comma
The Oxford comma (also known as the serial comma) is the comma used just before the conjunction ("and" or "or") in a list of three or more items. It helps clarify the meaning of a sentence by ensuring each item in the list is clearly separated.
Examples:
For dinner tonight, I will cook beef stew, new potatoes, green beans and ice cream. (Incorrect)
Without a comma, the green beans will be served with the ice cream.
For dinner tonight, I will cook beef stew, new potatoes, green beans, and ice cream. (Correct)
"I'd like to thank my parents, Oprah Winfrey and God." (Incorrect)
This implies my parents are Oprah and God.
"I'd like to thank my parents, Oprah Winfrey, and God."
The Oxford comma is not universally accepted. It often comes down to personal preference or the style / format being followed. However, its use can make certain sentences clearer and easier to read.
14. Colon errors
The colon is placed after a whole sentence to add a word, phrase, clause, list, or quotation. The colon signals that what follows proves or explains the sentence before a colon.
Examples:
Retired people move south for: warmer weather, the beaches, and cheaper retirement living. (Incorrect)
Retired people move south for three reasons: warmer weather, the beaches, and cheaper retirement living. (Correct)
In summer I like to eat: ice cream and fruit. (Incorrect)
In summer I like to eat two things: ice cream and fruit. (Correct)
15. Missing comma in a compound sentence
A common error occurs when two independent clauses are joined by a coordinating conjunction (such as "and," "but," "or," "so," "yet," "for," or "nor") but are not properly separated by a comma. This is another kind of run-on sentence.
When you have two independent clauses connected by a coordinating conjunction, a comma should separate them.
Example:
I understand that you need to work late nights but you really should find some time to relax. (Incorrect)
I understand that you need to work late nights, but you really should find some time to relax. (Correct)
16. Misplaced Periods
Periods with quotations:
Inside the quotation marks:
If the quoted material is a complete sentence, the period should be placed inside the quotation marks.
Example:
She said, "I'll meet you at the park."
Outside the quotation marks:
If the quoted material is not a complete sentence, the period typically goes outside the quotation marks.
Example:
He called it a "great idea".
Periods with parentheses:
Inside parentheses:
If the entire sentence or thought is enclosed in parentheses, the period should be placed inside the parentheses.
Example:
She went to the store. (I stayed home.)
Outside parentheses:
If the parentheses are part of a larger sentence and only enclose part of the sentence, the period should be placed outside the parentheses.
Example:
She went to the store (which is just a few blocks away).