Compare these two sentences: (A) "I'd like to thank my parents, Anna and the librarian." (B) "I'd like to thank my parents, Anna, and the librarian." What does the extra comma before 'and' in sentence B (called the Oxford or serial comma) actually change?
- In sentence A, without the extra comma, it sounds like the speaker's parents are named Anna and the librarian; the extra comma in sentence B makes clear that Anna and the librarian are two separate people being thanked in addition to the parents.
- The extra comma in sentence B is grammatically required in every sentence that lists more than two items, with absolutely no exceptions.
- The extra comma in sentence B changes the sentence from describing a past event to describing a present one.
- The extra comma in sentence B exists only to make the sentence easier to read aloud, and it makes no difference at all to what the sentence actually means.
Why A? And why not the others?
Correct answer: A. In sentence A, without the extra comma, it sounds like the speaker's parents are named Anna and the librarian; the extra comma in sentence B makes clear that Anna and the librarian are two separate people being thanked in addition to the parents.
Without a comma separating the final two items in a list, a phrase like 'my parents, Anna and the librarian' can be read as one single description — as though 'Anna and the librarian' is renaming or identifying who the parents are, the same way 'my favourite author, Jane Austen' identifies one person. Adding a comma before 'and', as in sentence B, breaks that reading apart and signals instead that the list contains three separate items: the parents, then Anna, then the librarian. That extra comma is the whole difference in meaning between the two sentences. It is not a universal grammar requirement — plenty of respected style guides deliberately choose to leave it out in most lists, treating it as a style choice rather than a rule with 'no exceptions'. It has nothing to do with verb tense, so it cannot shift a sentence from past to present. And it is not merely decorative for reading aloud either — as this exact pair of sentences shows, it can genuinely change who the sentence says is being thanked.
Source: Scribbr: 'Oxford Comma | Definition, Examples & When to Use'