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The comma is used to separate items in a list or phrases and clauses in a sentence, providing clarity and emphasis. This is a broad role, and therefore the comma is rather the jack-of-all-trades in the world of punctuation. As writer Lynne Truss states in her description of the comma as a “scary grammatical sheepdog,”

the comma has so many jobs as a “separator” (punctuation marks are traditionally either “separators” or “terminators”) that it tears about on the hillside of language, endlessly organizing words into sensible groups and making them stay put: sorting and dividing; circling and herding; and of course darting off with a peremptory “woof” to round up any wayward subordinate clause that makes a futile bolt for semantic freedom (Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation, Kindle edition; pp. 78-79).

Still, we can insist that commas, like sheepdogs, obey certain rules. Here are some of the most common ones that we at AsiaEdit encounter while editing.

Comma Before “And” in a List (i.e., Oxford Comma)

In a list of simple items, the comma is the basic unit of punctuation.

• “We measured the plasma concentrations of total cholesterol, triglycerides, and glucose.”

The exception is a list of complex items, which can be separated using semicolons (the rules of comma use still apply within each item!):

• “First, the enterprise is not digitally native; second, it is not a new venture; and third, it has begun to transform and has achieved initial results.”

The usefulness of the serial/terminal/Oxford comma (used in the first example after “triglycerides”) is debated. At AsiaEdit, our policy is to retain the author’s preferred style unless otherwise instructed by a style guide.

Comma Before “And” and Other Conjunctions (“But,” “So,”…)

A comma is not needed to separate two independent but related clauses that share a subject (i.e., a compound predicate).

• “Integrating other variables may improve the predictive power of the model and provide a more comprehensive understanding of tourist ERB.”

However, if the independent clauses have different subjects, a comma should be used to indicate the transition. In the statement below, this occurs after “alone.”

• “A firm’s innovation decisions are not dictated by TMTs alone, and both TMTs and MMs can influence each other by advocating or opposing innovation initiatives or deciding innovation directions.”

Commas with Restrictive and Non-restrictive Clauses

Commas can also be used to set apart non-restrictive clauses, which are parenthetical to the main statement (i.e., explanatory, rather than integral, clauses).

• “Various stakeholders, such as employers, service users, and the wider community, have higher expectations of graduates and schools.”
• “Fourth, the survey was conducted in China.”

However, they should not be used to set apart restrictive clauses that contain information integral to the main statement! In the statement below, no comma should be placed after “that.”

• “The study findings show that when patients were treated with a combination of chemotherapy and radiation, the survival duration increased by threefold.”

Thank you for reading. These tips were shared by the friendly managing editors at AsiaEdit!


Rachel, Louise, Leo, and Jennifer

Author Profile

Dr Jennifer Oliver
Managing Editor (Life Sciences)
After completing a PhD in Immunology at the University of Michigan and publishing several research articles as a first author or co-author, Jennifer began editing part-time while pursuing postdoctoral research in tumor immunology and radiology. She soon transitioned to full-time freelance work, with clients in various life science, biomedical science, and medical disciplines, before joining AsiaEdit full-time in 2016 and taking on her current role in 2020.

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