The comma, aside from its technical uses in mathematical, bibliographical, and other contexts, indicates the smallest break in sentence structure. It denotes a slight pause. Effective use of the comma involves good judgment, with ease of reading the end in view. Here are some guidelines.
The Comma in Dates.
Commas needed or omitted. In the month-day-year style of dates, the style most commonly used in the United States, commas are used both before and after the year. In the day-month-year system--sometimes awkward in regular text, though useful in material that requires many full dates--no commas are needed. Where month and year are only given, or a specific day (such as a holiday) with a year, neither system uses a comma.
- The ship sailed on June 12, 1910, for Southampton.
- The November 21, 1947, press conference elicited little new information.
- Smithers never regained his love of life. (See his journal entries of 3 July 1944 and 5 July 1953.)
- In December 1990 she turned seventy.
- On Thanksgiving Day 1998 they celebrated their seventy-fifth anniversary.
The Comma in Addresses and Names
Addresses and place-names in text. Commas are used to set off the individual elements in addresses or place-names that are run into the text. No comma appears between a street name and an abbreviation such as SW or before a postal code.
- Proofs were sent to the author at 933 Indian River Drive SE, Cocoa, FL 32922, on May 2.
- Cocoa, Florida, is not far from the Atlantic Ocean.
- The plane landed in Florence, Italy, this morning.
In a mailing address, commas should be used as sparsely as possible.
Personal names plus place-names. Commas are used to set off a place of residence immediately following a person's name unless the place is essential to the meaning of the sentence or is considered part of the person's name.
- Mortimer Snerd, of Woodland, was easily elected.
- Gerald Ford, from Grand Rapids, ascended to the White House.
- The Kennedys of Brevard County are unrelated to John F. Kennedy.
- Clement of Alexandria
"Jr.," "Sr.," and the like. Commas are no longer required around Jr. and Sr. If commas are used, however, they must appear both before and after the element. Commas never set off I, III, and such when used as part of a name.
- George W. Wilson Jr. has eclipsed his father's name.
- George W. Wilson, Jr., has eclipsed his father's name.
- John A. Doe III is the son of John A. Doe Jr.
"Inc.," "Ltd.," and the like. Commas are not required around Inc., Ltd., and such as part of a company's name. As with Jr., however, if commas are used, they must appear both before and after the element.
- The president of Bigco Electronics Inc. was the first speaker.
or, less desirably,
- The president of Bigco Electronics, Inc., was the first speaker.
We hope this was useful. Take another look at that document you're working on and make sure you're using commas properly.
Source: The Chicago Manual of Style.
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