Commas with Additional Information

Use a comma if the additional information is not part of the main statement.

Example: Thank you, ladies and gentlemen, for giving me the opportunity to speak to you today.

Note:

Depending on the importance attached to it, additional information can be enclosed in brackets, commas or dashes.

Brackets – not important

Connor (Amy's boyfriend) bought the tickets.

Commas – neutral

Connor, Amy's boyfriend, bought the tickets.

Dashes – emphasised

Connor–Amy's boyfriend–bought the tickets.

Use a comma in relative clauses before who and which if the information is not essential for the understanding of the sentence.

Example: Her brother, who lives in Chicago, came to see her.

Don’t use a comma in relative clauses if the information is essential for the understanding of the sentence.

Example: Her brother who lives in Chicago came to see her. 

Don’t use a comma if the relative clause starts with that.

Example: The book that I’m reading now is interesting.