Comma stock photos by Vecteezy

Commas can be tricky! I know this because they are one of the most frequent corrections I make when copyediting academic writing. This guide will help you to brandish your commas with confidence.

Covered in this blog post

Separating items in a series, joining independent (main) clauses, following a subordinate (sub) clause, following an introductory element, setting off an appositive, setting off a parenthetical expression, separating a nonrestrictive element, linking coordinating adjectives, following a dialogue tag to introduce a direct quotation

1. Separating items in a series

A serial comma (or Oxford comma) is inserted before the ‘and’ in a series of three or more items. Its usage is a matter of style (and, some would say, not strictly necessary for understanding a sentence), but my example below uses a serial comma because this follows APA Style.


In this study, I investigated how different teaching methodologies, classroom management strategies, and student engagement techniques affected academic performance in primary school settings.

Note: Turn on Word’s grammar checker by going to File > Options > Proofing, and then tick the box ‘Mark grammar errors as you type’. In that same section, open the Grammar Settings dialogue box, scroll down to ‘Punctuation Conventions’ and then tick the box ‘Oxford comma’.

See also:

2. Joining an independent (main) clause

You can spot an independent clause (also called a main clause) because it can stand on its own as a complete sentence. If you join two independent clauses with a coordinating conjunction (such as and, or, but, nor, yet, for, so), use a comma to separate them. I’ve highlighted the comma and coordinating conjunction in this example.


The study looked at how using technology in classrooms could improve student performance, and the findings showed that it had a positive impact on academic achievement.

Note: Instead of a comma, you could replace the comma and coordinating conjunction (‘and’) with a semicolon or an en or em dash.

See also:

3. Following a subordinate (sub) clause

A subordinate clause (also called a dependent clause or subclause) is a group of words that has both a subject and a verb and cannot stand alone as a complete sentence – it needs to be attached to an independent (main) clause to form a complete thought. In the following example, I’ve highlighted the subordinate clause that provides additional information.


The intervention, which aimed to improve reading proficiency among Year 3 students, involved tailored lesson plans and one-on-one tutoring sessions.

Note: The subordinate clause in this example is encased in a pair of commas, but you could also use en or em dashes or brackets.

4. Following an introductory element

An introductory element is a word or phrase that appears at the beginning of a sentence to provide context or to transition into the main clause. It often adds information or sets the stage for the rest of the sentence. In this example, I’ve highlighted the introductory element.


At the beginning of the research, a comprehensive literature review highlighted the existing gaps in understanding student motivation in online learning environments.

5. Setting off an appositive

An appositive is a noun or noun phrase that explains another noun in a sentence – it gives additional information about it, often helping to clarify it. Typically, appositives are set off by commas. In this example from the acknowledgements section of a doctoral thesis, the appositive is providing additional information about the advisor.


I would like to express my deepest gratitude to my advisor, Dr. Emily Thompson, a renowned expert in educational psychology, for her unwavering support and invaluable guidance throughout the research process.

6. Setting off a parenthetical expression

A parenthetical expression is a word or group of words that gives additional information and can be removed from the sentence without altering the grammatical structure. You would typically offset these expressions by parentheses (brackets), commas, or dashes, and I’ve given an example of each below.


The test results, conducted last month, indicated a significant improvement. (commas)

The test results (conducted last month) indicated a significant improvement. (parentheses)

The test results—conducted last month—indicated a significant improvement. (with em dashes in APA style)

7. Separating a nonrestrictive element

A nonrestrictive element is a word, phrase, or clause in a sentence that provides additional information – but it’s not essential, so removing an element like this from the sentence won’t alter its core meaning. To separate a nonrestrictive element, you might use commas, parentheses, or dashes.


My friend, who is a professor, shared valuable insights.

8. Linking coordinating adjectives

Coordinating adjectives (also known as cumulative or paired adjectives) are two or more adjectives that modify (or describe) a noun – they work together to give a more detailed and nuanced description of that noun. In this example, ‘clear’, ‘concise’, and ‘informative’ are coordinating adjectives that are modifying the noun ‘research paper’. Each adjective independently contributes to describing the qualities of the research paper.


The students wrote a clear, concise, and informative research paper.

Note: If you’re not sure when to add a comma, a trick is to ask yourself whether ‘and’ can be inserted between the adjectives. If the answer is yes, it’s usually safe to add a comma.


The students wrote a clear [and] concise [and] informative research paper.

9. Following a dialogue tag to introduce a direct quotation

The term ‘dialogue tag’ is commonly used to describe the part of a sentence that attributes or identifies the speaker. In the example below, ‘stated’ functions as a dialogue tag. Use a dialogue tag in writing to show who is speaking and to add variety to how you express the attribution.


One parent stated, ‘I believe that actively participating in my child’s education has a direct impact on their success in school.’

Note: ‘Reporting verb’ is another term for the part of the sentence that identifies who is speaking and how they are expressing themselves, particularly in scholarly writing. Other examples of reporting verbs include ‘said’, ‘mentioned’, ‘argued’, ‘explained’, ‘stated’, ‘suggested’ and so on.

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