Periods are pretty simple. They go at the end of a sentence when a statement is made, either declarative or imperative, and after an indirect question. Declarative sentences are those which state fact or observation. An imperative sentence is a type of non-urgent command. For example: Please take out the trash. Note even without the word please, this sentence would still be considered imperative, because there is no indication of anger or desperation. (If there were, an exclamation mark would be more appropriate.) An indirect question is a statement of a question someone else has asked. Indirect questions often start with "he asked" or "she asked" but do not have to.
Abbreviations, Parenthesis, and Lists
Periods are also used after abbreviations, such as "Mr." and Mrs." (except after cardinal directions). If a sentence has an abbreviation or quote with a period that falls at the end of a sentence, you do not put a second period after it. Example: The time is currently 8:01 p.m. Nevertheless, there is no hard and fast rule when it comes to using periods after all abbreviations. Some organizations prefer to exclude them, especially when all capital letters are used.
When using parenthesis, whether or not a period falls inside or outside depends on the context. If the information within the parenthesis forms a complete sentence, a period should be placed inside the parenthesis; an example of this can be seen in the first paragraph of this article. If the information within the parenthesis simply gives additional information but does not form a complete sentence on its own, a period should be placed outside the parenthesis (like in this sentence).
When making bulleted lists, periods should be placed at the end of each list item if complete sentences are used. Lists items that are fragments or single words do not require periods. However, your list should be consistent; use either complete sentences or fragments throughout your list, not both. For numbered and lettered lists, you will also need a period after each number or letter to set it apart from the items in the list.
Example 1:
While I'm away, my cat will need
- Food
- Water
- Fresh Litter
Example 2:
Writers should carry with them
a. Writing utensils
b. Erasers
c. A notebook
Example 3:
When you get stuck writing a scene,
- Take a break and come back to it later.
- Ask a friend for some input.
- Read some tips and articles for inspiration.
For more examples and further information on making lists, check out Grammar Girl's post: http://bit.ly/1eRzItD.
Quotations and Spacing
One of the most frequently asked questions involving periods is whether or not they go inside quotation marks. The U.S. has a very straight-forward rule on this: Periods alwaysgo inside quotations marks with no exceptions. Other countries, as well as the journalism field, do not follow this rule.
As far as spacing after a period--and any other ending punctuation--you should only put ONE space after it. In the days of typewriters, block letters (letters of an equal width) were used, so an extra space was needed to mark the beginning of a new sentence. However, with the introduction of word processors a few decades back, the ability to automatically detect different widths for each letter came about. This ability eliminated the need for the manual addition of an extra space. So question it no further: No matter how you were taught, it is now considered incorrect to use two spaces after a period. I realize this habit is difficult to break for a lot of people, and in truth, most people won't say anything if you use double spaces. The habit can be broken though!
Quick Overview of Periods
- Periods are used at the end of declarative and imperative sentences, and after indirect questions.
- Periods are used after abbreviations, except cardinal directions.
- There should only ever be one period at the end of a sentence.
- Periods can be placed inside or outside of parenthesis depending on the context.
- Periods are used after numbers and letters when making lists.
- For U.S. standards, periods always go inside quotations.
- Only one space should be used after a period.