In Sweden, it wasn’t until the late 1900s that scholars and practitioners started to agree on the key principle of when to use a comma. The trend these days is to use it less and less, and primarily to indicate pauses. The comma should help the reader rather than be used according to strict grammar rules.
As for English, the main comma-related conflict is still going strong and concerns the so-called serial or Oxford comma. A serial comma is a comma placed before the coordinating conjunction (usually and or or) in a series of three or more items:
- SLU offers programmes in agriculture, forestry, horticulture, and animal science.
The serial comma is more common in US than UK English. Only use it to clarify which are the actual list items if one of them contains the word and.
- The printing options available are greyscale, black and white, and colour.
And if you think a simple comma can’t possibly be that important, read about the missing comma that cost a US company 5 million dollars.
Below are some more examples of when to use or not use a comma.
Three examples of when to use a comma
1. Separating main clauses linked by a coordinating conjunction (and/but/or)
- The LTV Faculty is located in Alnarp, and the S Faculty is located in Umeå.
If both main clauses are very short, a comma isn’t always necessary.
2. Indicating supplementary elements
- This study, initiated by SLU researchers, showed that age was a significant factor.
3. To mark off introductory words
Use a comma to separate a single word or short phrase used to introduce a sentence:
- However, the arguments are unconvincing.
- On the other hand, the results speak for themselves.
Three examples of when not to use a comma
1. When two verbs share the same subject
Do not use a comma when a coordinating conjunction (and in the example below) connects two or more verbs to the subject of the sentence.
- They spent two years planning the project and raising funds for it.
No comma before and as they is the subject for both verbs.
2. Between two subjects performing the same action
- The author and the editor were both satisfied with the quality of the manuscript.
No comma before and as subjects that share a verb should not be separated.
3. Around restrictive clauses
A restrictive clause is a clause that is essential to the rest of the sentence (often introduced with that).
- The project that had been approved was granted funding.
Here, we are referring to one of several projects – the one that has been approved. The clause that had been approved is essential and cannot be removed. Do not use commas here.
Published March 2019.