common errors in all writing: commas

Haley Clapp November 7, 2025

1.

First, probably the most common error I see with commas is the overuse of commas when they are not needed.

This often happens because people add commas where they would naturally take a break when speaking a sentence out loud. While doing this might feel correct, I’m sorry to say that it often is not.

As a first guiding point, if the words that come after a coordinating conjunction (e.g., and, but, or) do not comprise a complete sentence (an “independent clause”), there should generally not be a comma before the conjunction.

Let’s look at an example:

Smith and Roberts (2023) reported that the acceptance of technology was high among their respondents, and that it was correlated with less technology anxiety. ❌

Because the latter phrase “that this was correlated with less technology anxiety” does not comprise a sentence that can stand on its own, the comma should be removed from this example.

Smith and Roberts (2023) reported that the acceptance of technology was high among their respondents and that it was correlated with less technology anxiety. ✔️

Let’s try another quick example:

This virus is considered a major contributor to the global decline in insect populations, and can be found in nearly every country. ❌

Here, again, the wording that follows the conjunction “and” cannot stand on its own as a complete sentence, so we would not use a comma.

This virus is considered a major contributor to the global decline in insect populations and can be found in nearly every country. ✔️

Be careful, though, to put the comma before, not after, the conjunction:

Caffeine increases the heart rate and, it constricts blood vessels. ❌

Caffeine increases the heart rate, and it constricts blood vessels. ✔️

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Hello! This is Haley C., and welcome to my first post in my new blog series, Common Errors in All Writing. In this series, I will be breaking down the most common errors I see in writing from writers of all proficiency levels (yes, even the experts!).

I’m calling this series Common Errors in All Writing because I’m going to be making a sister series after this one called “Common Errors in EFL Writing,” where I will break down the most common errors I see specifically in writing by EFL (English as a Foreign Language) writers.

In this post, I start with the biggest bear: commas.

Below are 5 common errors I see with comma usage in my everyday work.

I know even bringing up the matter of correct comma use is going to trigger a headache for some of you—just take a deep breath, and we’ll get through this together.

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Quick Definition

Independent Clause: An independent clause contains a subject and a predicate (verb phrase) and can stand by itself as a simple sentence.

2.

Next, a similar error I see is the use of a comma to split the subject and verb of a sentence. Don’t do it!

First, the study candidates, were all given a high dose of Vitamin B12. ❌

Here, the comma is splitting the subject “the study candidates” and its verb “were given,” so it should be removed.

First, the study candidates were all given a high dose of Vitamin B12. ✔️

This is similar to a generally applicable rule of thumb in grammar: subjects and their verbs want to be a close to each other as possible, with as little as possible in their way (including commas!).

 

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3.

Next, introductory phrases that begin with a preposition or adverb should always be followed by a comma. Some grammarians argue that a comma is not needed if the introductory phrase is short (e.g., 3 words or less), but I tend to disagree with this.

Quick Definition

Introductory phrase: A group of words at the beginning of a sentence
that introduce the action of the main sentence but cannot stand as a
sentence on their own.

Preposition: A word that shows how things relate to each other in time,
place, or purpose. It can also be used to introduce objects. Examples
include at, by, for, from, in, of, on, to, and with.

Adverb: A word that modifies (clarifies the meaning of) verbs,
adjectives, adverbs, or sentences. Adverbs answer the questions
when?, where?, how?, how much?, how long?, or how often?

Here are a few (correct!) examples:

In this study, we gave 50 participants a sorting task. ✔️

Despite the data limitations, we recruited an adequate sample size. ✔️

In light of these findings, we must question the validity of the proposed model. ✔️

Then, plates were added at a rate of ten per minute. ✔️

 

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4.

The next monster is the comma splice. A comma splice occurs when commas are used to split independent clauses.

To fix a comma splice, either add an appropriate conjunction (and, but, or) after the comma or use a semicolon or period instead of a comma.

Here are some examples and their corrections:

Participants in the experimental group were given 100 mg of aspirin, participants in the control group were given a placebo. ❌

Participants in the experimental group were given 100 mg of aspirin; participants in the control group were given a placebo. ✔️

Participants in the experimental group were given 100 mg of aspirin, and participants in the control group were given a placebo. ✔️

The first trial was inconclusive, the second provided clearer findings. ❌

The first trial was inconclusive; the second provided clearer findings. ✔️

The first trial was inconclusive, but the second provided clearer findings. ✔️

 

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5.

Last but certainly not least, we have the Oxford (or serial) comma. The ‘debate’ over whether to use the Oxford comma is one of the most well known among grammarians, but as far as I’m concerned, there is no debate: the Oxford comma is the way to go.

But what is the Oxford comma?

An Oxford comma is a comma that appears before the last conjunction (and, but, or) in a series where three or more items are listed, as in the below example:

The group coordinates community bake sales in spring, fall, and winter. ✔️

In that sentence, the Oxford comma is the final one in the sentence, before “and winter.”

Okay, so what’s the big deal?

Below is an often-cited example sentence used to illustrate the problem with omitting the Oxford comma:

I’d like to thank my parents, the Queen and the Pope. ❌

In this sentence, the Oxford comma is not used. (If it were, its appropriate location would be before the conjunction “and” before the final item in the list.)

However, without using the Oxford comma, this sentence could be misread as saying your parents are the Queen and the Pope, as in, “I’d like to thank my parents, who are the Queen and the Pope.”

That’s a big yikes. The easy fix? Add the comma!:

I’d like to thank my parents, the Queen, and the Pope. ✔️

As this example clearly shows, not using the Oxford comma can raise major issues in terms of clear communication and interpretation.

In fact, the omission of the Oxford comma has been of such significance that it has caused legal issues and controversy, with more than one legal case hinging entirely on the correct interpretation of text where an Oxford comma was not included. This includes, perhaps most notably, a >$10 million lawsuit in front of the United States Court of Appeals.

While your not adding an Oxford comma might not cost you such a pretty penny, it can still lead to fundamental misinterpretations of your meaning—which can be just as dangerous depending on your field.

So, the bottom line: Use the Oxford comma! It will always be correct.

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I hope these five examples have been helpful in illuminating some common comma errors. My next installment will be in an area that (hopefully!) causes less stress: colons and semicolons. Stay tuned, and thanks for reading!

Want someone else to worry about your commas (and everything else)? Check out my Services for more information on what I offer or Contact Me for any questions or to get started on a project together.