Periods  

The period (also known as a full stop, especially in British English) is a punctuation mark primarily used to indicate the end of a sentence. It appears as a single dot on the bottom line of the text ( . ), and it comes immediately after the last word of the sentence without a space.

There are also several minor uses for the period, which we’ll look at later in this section.

The most common use of periods is to punctuate the end of sentences. This occurs with almost all the types of sentences we use. For example:

Note that if we wanted to indicate an especially strong emotion in any of the above sentences, or else indicate that the speaker is shouting, we would typically use an exclamation point instead. For instance:

However, this is based solely on the intention of the writer; the form of the sentence itself doesn’t require that an exclamation point be used instead of a period.

The only type of sentence in which a period is not used is the interrogative sentence (a sentence that asks a question). These sentences always use question marks rather than periods, as in:

If a sentence uses quotation marks to indicate something that another person has said, and the quotation marks appear at the end of the sentence, the period can appear in one of two places.

In American English, the punctuation used at the end of direct speech always appears within the quotation marks. For example:

However, in British English (which also uses different rules for quotation marks), periods that end quotations are usually placed outside the final quotation mark, as in:

When we begin a new sentence after another one has ended, we generally use a single space between the period of the first sentence and the first word of the second sentence.

However, at one point, it was standard practice to add two spaces after the end of a sentence. This trend arose out of the use of manual typewriters (in which the monotype font created a lack of space between periods and the first letter of the next sentence). With the advent of word processor applications for computers, this problem was eliminated, but some writers today persist in adding two spaces after a period.

While this continues to be a point of contention for some, the definitive answer is that it is not only preferable but correct to use only one space after the period of a sentence. This is a point on which all modern grammar and style guides (including this one) agree: when beginning a new sentence after a period, only use a single space.

While the period is most commonly used to mark the end of a sentence, it is also used to mark abbreviations. In addition to standard abbreviations (words that are shortened by omitting one or more letters), there are also three sub-categories that can use periods: initials, acronyms, and initialisms.

However, unlike its use in punctuating the end of a sentence, the use of a period with abbreviations is not as strict or consistent, often depending on the location (i.e., American English vs. British English) and preference of the writer, publisher, or style guide.

We often use periods to indicate when a word has been abbreviated (that is, has had letters omitted from it) in a sentence. This period always appears at the very end of the abbreviated word. For example:

Note that when an abbreviation ends a sentence, the period that shortens the word also marks the end of the sentence—that is, we do not use a second period. If another punctuation mark (such as a comma or question mark) is used after an abbreviated word, it comes directly after the period. For example:

Formal titles, such as Mr., Mrs., or Dr., are actually abbreviations, but we usually only use them in their contracted forms in writing. Because they are so common, the period is usually left out in British English, as the abbreviation does not need to be indicated by punctuation to be understood. It’s therefore common to read “Mr Jones,” “Mrs Smith,” or “Dr Casey” (for example) in writing that uses British English styles.

In American English, however, these abbreviated titles are still punctuated with periods.

Initials are a kind of abbreviation of people’s names formed from the first letter of each part of the name (first, middle, and/or last name). We usually mark each initial with a period. For example:

If sequential parts of someone’s name are made into initials, then a space will usually come after the period of the initial. For example:

However, while some style guides recommend this spacing between letters, other style guides recommend not including spaces, as in:

Whether to use spaces after the periods of initials is largely a matter of personal preference, but be sure to check the recommendations of your school’s or employer’s style guide.

(Note: It is also not uncommon to see multiple initials used without either periods or spaces, as in “JRR Tolkien,” but this usually occurs in less formal writing.)

Similar to initials, acronyms and initialisms are abbreviations of multiple words using just their initial letters.

Acronyms are distinguished by the fact that they are read aloud as a single word. Because of this, they are usually (but not always) written without periods. In some cases, the acronym has become so common that the letters aren’t even capitalized anymore.

For example:

Initialisms are formed in the same way as acronyms, but they are spoken aloud as individual letters rather than a single word. (However, because they are so similar in appearance to acronyms, initialisms are very often simply referred to as acronyms.)

Like acronyms, it is most common to write initialisms without periods. However, in American English, it is also common to include periods between the letters of some initialisms. This varies between style guides, and it is generally a matter of personal preference; whether you use periods in initialisms or not, be sure to be consistent.

Here are some examples of common initialisms (some with periods, some without):

One final common use of the period is as a decimal point—the dot that separates a whole number from its decimals. For example: