Periods are at first glance a simple punctuation mark, yet in certain contexts they fall with a dramatic weight like a scroll with a prophecy falling unseen past jagged cliffs to join the abluvion. Like the first bolt of lightning to hit the valley. Like the unfurling of Rainfall’s wings as she makes her escape. They are often ignored, but we cannot do without them (except in text messages). They also stage an occasional appearance in abbreviations.
Spacing and typography Except in usernames and URLs, a period is always followed by a space (or occasionally two after a sentence). In abbreviations, spaces are optional.
Statements A period is used at the end of a declarative sentence (a statement): It was a dark and stormy night.
Sentence fragments A period is also used at the end of a sentence fragment, which is basically a sentence to all except those who insist on having both a subject and a verb. They’re sometimes considered nonstandard (so you may want to avoid them in school assignments), but they’re acceptable in most contexts, especially informal and creative writing. The perfect time to stage her escape. (No predicate, since to stage is like a noun here.) Abandoned her role in the path of the world. (No subject.) So dark and stormy. (Neither.) Same with the parentheticals, and with this sentence! See, aren’t sentence fragments fun?! However, a clumsy one can be distracting, so it’s good to take note of when you use them. Watch out especially for dangling participles
Dramatic effect After a short sentence or fragment, a period is often used in creative writing for dramatic or ominous effect: It was the perfect night for her escape. Rainfall’s wings blended into the dark gray of the clouds, almost invisible. Almost. (See also Ending Sentences and Sentence Length.)
Emphasis They can be used between words for emphasis: They. Will. Not. Win. (Capital letters are optional informally.)
Anger and disdain A period can also be used to express things like frustration, disdain, sarcasm, or anger, as Rainfall likely is using them now. However, it largely depends on the context and the reader’s interpretation (and perilously so!). A question or exclamation ending with a period generally does: Wow, thanks. Now what am I going to do. In informal conversations, it can sometimes sound angry and sarcastic (it largely depends on the person and their demographics) at the end of a phrase like see you soon or great, I’m looking forward to it. [examples here] But one never knows (except when one does). See also Exclamation Point/Exclamation Mark.
Abbreviations A period is used after abbreviations such as Ms./Mr./Mx. in American English (no punctuation is used in British English), and after each letter in ones like i.e. and a.m. (the latter is often written as AM), but only in words like lol and ok if you want to sound like a wise, ancient being. The use of periods and/or caps in abbreviations is pretty random, so if you’re unsure, consult your preferred dictionary or style guide. But for reference: i.e., e.g., a.m./AM/A.M., etc., ibid., Mx., Jr. Acronyms are usually in all caps (formally) or lowercase (informally) without periods, but periods can be used as well. And some abbreviations, for inexplicable reasons, use slashes.
Time In British English, they’re used to separate hours, minutes, and seconds: 12.17. (In American English, colons are used instead.)
Decimals They’re used in decimals: 3.14159.
Lists They’re used in numbered or lettered lists:
- Escape the valley
- Let out a breath I very much know I am holding
- Find the enchanted forest
Internet They’re used in usernames, email addresses, and URLs, as you have likely observed.
Ellipses Formally, three periods separated by nonbreaking spaces (with a space on either side) form an ellipsis (see Ellipsis); informally, you can use any number with any spacing: She kept flying as the sky lightened…. if only she knew where she was going…..
Placement See Quotation Marks, Parentheses, Brackets, and Ellipsis for use with those punctuation marks.