A comma is a punctuation mark used to indicate division.
The comma mark is: ,
- subordinate clauses before the main clause
- If you need help, please don’t hesitate to contact us.
- When you ask your mum for permission, let us know if you will come.
- Shall you have any technical problems, let us know and we’ll try to solve them.
- non-defining clauses
- My brother, who is eight years old, can swim well.
- Warsaw, which is in Poland, was destroyed in World War II.
- The flood, lasting three weeks, damaged a lot of houses.
- Parenthetical commas
- Tom got ready to go to the party with big excitement.
- Tom, with big excitement, got ready to go to the party.
- Tom got ready, with big excitement, to go to the party.
A comma is used:
- separating the subordinate clause from the main clause when the subordinate clause goes before the main one.
- in non-defining clauses that add extra (and non-necessary) information are always between commas.
- Parenthetical Commas: extra information that is between commas and can be placed anywhere in the clause
External link to Comma exercises (1250).