A missing subject, a clunky structure, or wrong punctuation. Sentence errors are easy to miss, especially if you don’t know what to look out for. But that’s all going to end today because you’ll discover the most common sentence mistakes and how you can correct them with AI’s help.
1. Fragments
Fragments are sentences that have been cut off in the middle of a thought. They lack something, often a subject, verb, or whole idea.
A sentence fragment often shows up when you’re breaking up longer sentences or adding emphasis. Sometimes, they work stylistically, but if the meaning isn’t clear on its own, it needs to be revised.
Example: Because I was tired.
That is not a complete sentence. It leaves you suspended. Because you were tired, what?
To fix it, complete the idea: Because I was tired, I didn’t finish my homework.
You are a proofreader. Please review my sentences below and determine if they are sentence fragments. If they are, please offer suggestions on how to correct it.
[insert your sentence] 2. Run-Ons
Do you know what happens if you combine two or more independent clauses without punctuation or a connecting word? You create a run-on sentence, which blurs your ideas and makes sentences harder to follow
Example: She submitted the article it was published the next day.
These are two full thoughts, but there’s nothing linking them.
To fix a run-on sentence, you can:
- Split it into two sentences
- Add a conjunction (and, but, so)
- Use a semicolon
The fix depends on how you want the sentence to flow, but clarity should always come first.
You are a proofreader. Please check my sentences below if they are run-on sentences. If you found any, please offer suggestions on how to correct it.
[insert your sentence] 3. Comma Splices
A comma splice, a type of run-on, happens when you use a comma to combine two independent clauses.
Example: He loves writing, he spends hours at his desk.
The comma here should either be a period or a semicolon. You can also have a conjunction.
It’s an easy mistake because the sentence sounds right when read aloud. But in writing, it’s grammatically incorrect. Fixing it improves readability and avoids confusing your reader.
You are a proofreader. Please check my sentences below for correct comma splice use. If you found any, please offer suggestions on how to correct it.
[insert your sentence] 4. Subject-Verb Agreement
The verb in your sentence has to match the subject in number: singular with singular and plural with plural. But things get tricky when extra words appear between the subject and the verb.
Example: The group of students are meeting in the library.
Group is singular, so the verb should be is, even though students is plural.
Watch out for:
- Prepositional phrases that distract from the real subject.
- Collective nouns like team, audience, staff, etc.
- Sentences that start with there is or there are.
You are a proofreader. Please check my sentences below if the subject agrees with the verb. If it doesn't, please offer suggestions on how to correct it.
[insert your sentence] 5. Too Long
When a sentence tries to do too much, it loses clarity. The main point gets buried under extra clauses, filler words, or over-explaining.
Example: Despite the fact that she had already completed the report ahead of schedule, which was unusual, she decided to go over it again just in case there were still some unnoticed mistakes that could affect the final version.
If you’re forcing your reader to reread, the sentence is probably too long. The best action is always to simplify.
You are a proofreader. Please check my sentences below if it is too long. If it is, please offer suggestions on how to correct it.
[insert your sentence] 6. Dangling Modifier
Do you have a descriptive phrase that doesn’t connect to what it is supposed to in the sentence? That’s a dangling modifier.
Example: Walking into the room, the silence was deafening.
Wait… did the silence walk into the room?
These mistakes usually happen when you’re trying to add variety or set the scene. But if the subject isn’t clearly stated, you’ll leave readers raising their eyebrows.
You can fix it by clarifying the subject: When I walked into the room, the silence was defeating.
You are a proofreader. Please check my sentences below if there is a dangling modifier. If you found any, please offer suggestions on how to correct it.
[insert your sentence] 7. Faulty Parallelism
Having a parallel structure means keeping patterns consistent, especially when listing ideas or linking similar thoughts. But when the structure changes halfway through, it’s a grammatical mistake, and the sentence feels uneven.
Example: He likes running, to swim, and biking.
That list mixes gerunds (running, biking) with an infinitive (to swim).
The correct way would be: He likes running, swimming, and biking.
When your sentence structure matches, the writing flows better and is easier to read.
You are a proofreader. Please check my sentences below for faulty parallelism. If you found any, please offer suggestions on how to correct it.
[insert your sentence] 8. Incomplete/Faulty Comparisons
When comparing things, both clauses should be present; If not, you leave your reader guessing, and can lead to misunderstandings.
Example: Her skills are better.
Better than what? You may understand what you’re saying, but your reader doesn’t.
To fix these, finish the comparison: Her cooking skills are better than Jane’s.
You are a proofreader. Please check my sentences below for incomplete or faulty comparisons. If you found any, please offer suggestions on how to correct it.
[insert your sentence] 9. Pronoun Reference & Agreement Error
A pronoun needs to refer to a specific noun, and it has to match in number and gender. If not, your sentence becomes confusing or ambiguous.
Example of unclear reference: When Sam told Jamie she got the job, she was thrilled.
Who was thrilled? Sam or Jamie?
Example of an agreement issue: Each boy must bring their notebook.
Each boy is singular, but their is plural.
Fix it with either clarity or consistency:
- Sam was thrilled when she told Jamie about the job.
- Each boy must bring his notebook. (Or rewrite in plural: All boys must bring their notebooks.)
Tip: Readers should never have to pause to figure out who you’re talking about. Pronouns should do their job: point clearly and match smoothly.
You are a proofreader. Please check my sentences below for pronoun reference and agreement errors. If you found any, please offer suggestions on how to correct it.
[insert your sentence] 10. Verb Tense Shifts
Shifting tenses mid-sentence or mid-paragraph without a reason throws off the reader.
Example (Incorrect): He studied all night, then opens his laptop and starts the exam.
The shift from past to present makes it hard to track the timeline.
If you’re telling a story in the past tense, keep it there, unless you need to switch for effect or clarity. Tense should follow the logic of the narrative, not your last round of edits.
You are a proofreader. Please check my sentences below for verb tense shifts. If you found any, please offer suggestions on how to correct it.
[insert your sentence] 12. Double Negative
If you have two negatives in one sentence, they cancel each other out and turn the sentence into a positive one. Sounds confusing, right?
Example: I don’t need no help.
You probably meant you do need help, but that sentence says the opposite.
Double negatives are pretty common in informal speaking, mostly in American English, but when used in formal writing, they can confuse the reader. So it is best to avoid them.
You are a proofreader. Please check my sentences below for double negatives. If you found any, please offer suggestions on how to correct it.
[insert your sentence] 13. Overuse of Passive Voice
Passive voice isn’t inherently a problem—it becomes one when it’s used in situations where active voice would be simpler and more clear.
Example: The report was written by the manager.
Why not just say, “The manager wrote the report”?
To spot passive voice, look for forms of “to be” (was, were, is, are) followed by a past participle. If the sentence feels distant, try flipping it around to focus on who’s doing the action.
You are an editor. Please check my sentences below and change the voice from passive to active when appropriate.
[insert your sentence] 14. Lack of Sentence Variety
Even well-written sentences can lose impact if they all follow the same pattern.
Example: She finished the draft. She sent it to the editor. She waited for feedback.
There’s nothing technically wrong, but it reads like a list.
You are an editor. Please check my sentences below and determine whether or not they lack sentence variety. If there is, please correct it.
[insert your sentence] 15. Incorrect Subordination
Subordination connects a dependent idea to a main one, showing how they relate. The issue comes when that relationship is unclear, or when a dependent clause is left standing on its own.
Example: Although the storm was intense. We kept driving.
The first sentence isn’t complete. It needs the second part to make sense.
Corrected: Although the storm was intense, we kept driving.
You are a proofreader. Please check my sentence below if there is an incorrect use of subodrination. If there is, please explain why it's wrong and how to correct it.
[insert your sentence] 16. Incorrect Use of Conjunctions
Conjunctions connect ideas, but using the wrong one can quickly turn your sentences into a hot mess.
Example: I was tired, but I went to bed early.
This sounds fine, but but suggests contrast. There’s no contrast here; being tired explains why they went to bed.
It should be: I was tired, so I went to bed early.
Some common mix-ups:
- But vs. so (contrast vs. cause)
- Although vs. because (opposition vs. reason)
- And used to link unrelated thoughts
You are a proofreader. Please check my sentence below if there is an incorrect use of conjunction. If there is, please explain why it's wrong and how to correct it.
[insert your sentence] Clear Writing Doesn’t Have to Be Complicated
Achieving perfect and clean sentences is easier said than done. The good news is that you don’t have to fix sentence mistakes alone. AI can be your sentence corrector and grammar checker so that you can save a lot of time and energy on your next essay, book, or article!