The period, called a full stop in British English, is one of the first punctuation marks we learn about when we begin reading and writing. Compared to commas or semicolons, the rules for using periods are blessedly simple.
What Does a Period Do?
The most common use of the period is, of course, to end a declarative sentence. Interrogative sentences (questions) end with a question mark.
Periods and Quotation Marks
When writers get confused about periods, it’s usually because they aren’t sure where to put them in relation to other nearby punctuation. In American English, the period goes inside the closing quotation mark at the end of a sentence.
Periods and Parentheses
When a complete, independent sentence is entirely enclosed by parentheses, the period goes inside the closing parenthesis.
But, if the parenthetical material is nested inside another sentence, the period should go on the outside.
An ellipsis (plural: ellipses) looks like three periods in a row. There are two main uses for ellipses. One is to show that part of a quote has been omitted.
In the sentence above, the words “in the mind” have been omitted from the quote. Occasionally, you might need to leave out part of a quote because it’s irrelevant or makes the quote hard to understand in the context of the sentence. The ellipsis shows that you have left something out.
You can also use an ellipsis for literary effect, to represent a dramatic pause or a thought that trails off. Sometimes, this type of ellipsis is also referred to as “suspension points.”
This usage is fine in fiction, but you should avoid it in formal writing.