Serial commas

Writers often wonder whether to use a serial comma (that is, a comma before the last item in a series).

When to omit the comma

In keeping with the trend toward less punctuation, we suggest you generally omit the serial comma, as in the following example:

• We Canadians are standing on the mountaintop of human wealth, freedom and privilege.
  —Pierre Elliott Trudeau

When to use the comma.

However, do include the comma if it is necessary for clarity or emphasis.

• For clarity:
  • Joe's favourite sandwiches are tuna, ham, and cheese.
  • Joe's favourite sandwiches are tuna, ham and cheese, and bacon.
    
    [In each case, the comma shows whether cheese goes with bacon or with ham.]
• For emphasis:
  • She embraced him once again, turned away, and then walked out the door forever.
    
    [The comma after turned away could be omitted, but here it is used for emphasis.]

In preparing this linguistic reminder, we consulted the following sources:

Guide to Canadian English Usage (2nd ed.)
The Canadian Style: A Guide to Writing and Editing
The Oxford English Grammar