9 Common Punctuation, Grammar, and Other Mistakes I See as a Copyeditor 

I have always had an instinct and natural talent for spotting and correcting errors in sentence structure. Even as a teenager, I could easily correct other people’s writing without even knowing the “technical” terms for what I was seeing and doing. 

Like many English speakers with this talent, I didn’t (and still usually don’t) consciously think of the technical terms for the errors when I see and correct them. Perhaps it's a result of the K-12 education system, and the fact that some teachers didn’t teach (and perhaps didn’t know) the technical language of grammar and punctuation. 

The pedagogical idea at the time was that we would learn how to write well organically, through reading and writing practice. Some of us (like me) with a talent in this area did well, but others struggled. At university, I once met a primary school teacher who didn’t know what a conjunction was. 

Anyway, let me get to the point. I just know when a sentence is wrong or could be improved and exactly how to fix it, but it can be helpful to know what the errors are called, so you can stay more conscious of them when you’re writing and editing.

That is why I’ve put together this list of the 9 most common punctuation and grammar mistakes I see in the writing of my copyediting clients.

1. Comma Splice (Run-On Sentence) 

If you use a comma to join two clauses that each have a subject and a verb, that is a comma splice, otherwise known as a run-on sentence. 

Here are some examples. 

Wrong: 

Anna went to the mall, she went to the park the next day. 

Correction: 

Anna went to the mall. She went to the park the next day. 

2. Subject-Verb Disagreement 

Subject-verb disagreement is one of the most immediately noticeable grammar errors. 

Wrong: 

Anna swim every day. 

Correction: 

Anna swims every day. 

Anna (the subject) is singular, but swim is the form of the verb to use with a plural subject. Instead, you should use swims. 

Wrong: 

The government were making decisions. 

Correction: 

The government was making decisions. 

Note: This one is trickier and can vary between US and UK English. In modern UK English, we often see collective nouns like “government” being used as plural rather than singular. 

Wrong: Ted and Ryan is traveling. 

Correction: Ted and Ryan are traveling. 

Ted and Ryan make a plural subject, and so you should use the plural form of be, which is are. 

3. Using the Simple Past When You Need the Past Perfect 

This is one of my pet peeves. Here are some examples. 

Wrong: I have wrote a letter.

Right: I have written a letter, or I wrote a letter. 

Written is the past perfect form of the verb. Wrote is the simple past version. 

Just remember, you need to use the past perfect form of the verb if you use “have” before it. 

4. Misplaced and Dangling Modifiers 

A modifier is a part of a sentence that modifies another part of the sentence. A good rule of thumb is that the modifier should always be as close as possible to what it is modifying. A misplaced modifier is when the modifier is further away from the element it is modifying than it has to be. A dangling modifier is a modifier in a sentence that lacks the element you meant it to modify. 

Wrong: 

Betsy ran around the block with a red jacket. 

This sentence has a misplaced modifier (with a red jacket). The way the sentence is worded makes it seem as if the block rather than the person has the red jacket. 

Correct: 

Betsy wore a red jacket when she ran around the block.  

Wrong: 

Kate sings in the choir with a clear and melodic voice. 

This sentence has a misplaced modifier (“with a clear and melodic voice”). It is unclear whether Kate has the clear and melodic voice or if the choir has that voice. 

Correct: 

Kate has a clear and melodic voice, and she sings in the choir. 

Wrong: 

Wearing a purple shirt, the dog trotted over to see Amy.  

This sentence has a misplaced modifier. We can’t tell if Amy or the dog is wearing the purple shirt. 

Correct: 

Amy was wearing a purple shirt when the dog trotted over to see her. 

Wrong: 

Having gone to the mall, the theme park was a lot of fun. 

This is incorrect because it seems like the theme park went to the mall, not a person. 

Correct: 

After visiting the mall, we went to the theme park and had a lot of fun.

5. Misplaced and Missing Commas 

Commas can be quite tricky because what is considered correct usage varies from country to country and even style guide to style guide. For example, in the past, UK English featured heavy comma use. Today, the opposite is true. In fact, if you look at many books published in the UK today, you will spot some instances of what we would consider missing commas in North America. For example, I have seen books (from publishers like Oxford University Press, etc.) with a comma missing after the word “Today” at the beginning of the sentence.  

Most native English speakers know instinctively where to put commas. Generally speaking, we can put them where we take a breath when reading something out loud. Here are some of the kinds of sentences where we would use commas. 

After an introductory adverb: 

Clearly, he has never been to South America. 

Between a complete clause (clause with subject and verb) and another clause when joined by a coordinating conjunction (such as and): 

For example: 

I visited the museum yesterday, and I enjoyed it.  

Wrong: 

Today I cooked a delicious breakfast. 

Correct: 

Today, I cooked a delicious breakfast. 

Wrong: 

Elephants are enormous, animals and they have big ears. 

Correct: 

Elephants are enormous animals, and they have big ears. 

6. Misplaced Apostrophes 

Make sure you know where the apostrophe should go when you need to use one. The two main uses for apostrophes are adding an “is” to a word and creating a possessive. 

Let’s take a look at it’s/its. 

It’s/Its

Many people get confused about when to use it’s and its. 

You must use it’s when you are combining it and is. On the other hand, its is possessive. 

7. Wordiness

General wordiness is probably one of the most common things I need to correct for my copyediting clients. Using too many words makes your writing less engaging and will make your work less enjoyable to read. 

8. Diction (Word Choice) 

Be aware of the denotations and connotations of words. Poorly chosen vocabulary is a common problem with many writers. Be mindful of the words you choose, and if you’re not absolutely certain of a word’s denotation and connotations, look it up in a dictionary. 

9. Awkward Sentence Structure 

Awkward sentence structure covers a multitude of errors, as well as wordiness. Remember, flow is one of the most important characteristics of your writing. 

I recommend reading your work aloud. If it sounds convoluted or strained, you probably need to rewrite your sentence. 

Looking for a skilled copyeditor? I’m available to hire. Contact me via https://www.samanthalordwriter.com/contact-me, and we’ll get started on your project! 

(I also published this article in my Substack newsletter, Reflections by Samantha Lord.)