Q. Hello. In the sentence “I went to the store to buy eggs, milk and cheese” do you put a comma after “milk”? What is the standard now for comma usage after the second-to-last item? I have seen such sentences both with and without the comma. Thanks.

A. Chicago style is to put a comma there (it’s called a “serial” comma). There are times when that comma is necessary to avoid awkwardness or ambiguity: “My favorite combinations are green and yellow, blue and purple and black and red.” Since it is sometimes needed, and is never wrong, the simplest way to impose consistency without having to stop and think about each instance is to form a habit of adding the serial comma.