When to use a comma in academic writing
Most comma decisions come down to a handful of rules. Here they are, with examples drawn from the kind of sentences you write in essays and dissertations.
Use a comma before a conjunction such as and, but or so when it joins two complete sentences, after an introductory phrase, around extra information the sentence could lose, and between items in a list. Do not put one between a subject and its verb, and never use a comma alone to join two complete sentences. Those rules answer almost every question about when to use a comma in academic writing.
Commas matter more than their size suggests. A misplaced one can change which part of a sentence a claim applies to, and frequent comma errors tell a marker that the work was not proofread closely.
When to use a comma: seven rules
1. Before a conjunction joining two sentences
When and, but, or, so or yet joins two clauses that could each stand alone as a sentence, put a comma before the conjunction.
Example
The survey closed in May, and the interviews began in June.
With very short clauses, many writers leave the comma out. In academic writing, keeping it is the safer habit.
2. After an introductory phrase
Put a comma after a word, phrase or clause that comes before the main part of the sentence.
Examples
In the second phase of the study, participants kept a diary.
Although the sample was small, the effect was consistent.
Very short openers, such as In 2024, can go without a comma. Whichever you choose, be consistent.
3. Around information the sentence does not need
If you could remove a phrase and the sentence would still mean the same thing, put commas on both sides of it. If removing it would change the meaning, leave the commas out.
Extra information, so commas
The second survey, which ran for six weeks, had a higher response rate.
Essential information, so no commas
Participants who withdrew were excluded from the analysis.
In the second sentence, who withdrew tells you which participants were excluded. Take it away and the sentence says every participant was excluded.
4. Between items in a list
Separate three or more items with commas. Whether a comma also goes before the final and is a style choice, covered below.
Example
The questionnaire covered age, income, housing and employment.
5. Between adjectives that each describe the noun
If you could put and between two adjectives, separate them with a comma. If and would sound wrong, leave the comma out.
Comma
a long, detailed report
No comma
a qualitative research design
6. In large numbers
Most UK styles use a comma in numbers above 999, such as 1,200 participants or 10,000 words. British dates, such as 14 September 2026, need no comma at all.
7. Never between a subject and its verb
However long the subject grows, do not separate it from its verb with a single comma.
Wrong
The number of students who reported high stress during the examination period, rose sharply.
Right
The number of students who reported high stress during the examination period rose sharply.
Put a comma before and only when it joins sentences
Whether a comma goes before and depends on what and is joining. Between two complete sentences, use one. Between two verbs that share a subject, leave it out, as in: the team collected the data and analysed it. Before the last item of a list, the answer depends on the Oxford comma.
Decide on the Oxford comma
The Oxford comma is the comma before and or or at the end of a list, as in red, white, and blue. It is also called the serial comma or the Harvard comma. In British English it is optional. Many UK newspapers leave it out, while Oxford University Press, which gave it the name, keeps it.
Occasionally it removes a real ambiguity.
Ambiguous
I thank my parents, Dr Patel and Dr Evans.
Clear
I thank my parents, Dr Patel, and Dr Evans.
Without the Oxford comma, the first sentence could mean that Dr Patel and Dr Evans are your parents. Check whether your department's style guide sets a rule. If it does not, pick one approach and apply it through the whole document.
Fix a comma splice
A comma splice is two complete sentences joined only by a comma. It is the comma error markers flag most often, and our guide to common grammatical errors covers it alongside other frequent mistakes.
Wrong
The results were significant, the sample was small.
Right
The results were significant, but the sample was small.
The results were significant. The sample was small.
A semicolon also works when the two ideas are closely linked. Ourcolons and semicolons guide explains when that is the better choice.
Check the commas in a draft
Read the draft aloud, slowly. Pauses are not a reliable guide on their own, but an awkward stop often exposes a comma between a subject and its verb, and a sentence that runs on too long often hides a comma splice. Then search the document for which and however, because both nearly always need a decision about commas.
Grammar checkers catch some comma errors, miss many others and suggest a few that are wrong, so treat their flags as prompts to look again. Apostrophes are the other punctuation mark that survives into final drafts, and our possessive apostrophe guide covers them.
If you want every comma checked, our proofreaders correct punctuation throughout your document in tracked changes, so you can see each correction and learn the pattern.
Last updated: 14 September 2026 · Written by the AssignWise editorial team ·Spotted something wrong?
Frequently asked questions
Put one before and when it joins two complete sentences, as in: the survey closed in May, and the interviews began in June. Leave it out when and joins two verbs that share a subject. Before the last item in a list, it depends on whether you use the Oxford comma.
Yes, and so is leaving it out. The Oxford comma, also called the serial or Harvard comma, is optional in British English. Many UK newspapers omit it, while Oxford University Press uses it. Follow any department style guide, and use your choice consistently.
A comma splice joins two complete sentences with only a comma. Fix it with a full stop, a semicolon, or a conjunction such as but or so after the comma. It is one of the errors markers flag most often in student writing.
Yes, when however opens a sentence and means nevertheless: However, the effect was small. When however links two complete sentences, put a semicolon or a full stop before it and a comma after it. Commas alone on both sides create a comma splice.
Usually. Which normally introduces extra information that could be removed, and that information sits between commas. When the information identifies exactly which thing you mean, British English often uses that instead, with no comma.
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