Where do commas go in the vicinity of references to city and state names, or when identifying a date? Is a comma necessary before Jr. or II after a person’s name, or between a corporate name and a tag like Inc.? The rules for use of such functional punctuation follow:
1. City-and-State Designations
In a city-and-state (or city-and-nation) construction, the state is set off from the city by a pair of commas: “A point near Rugby, North Dakota, is the geographic center of North America.” However, when describing an address, no comma appears between the state name or abbreviation and the ZIP code: “He listed his address as 1600 Pennsylvania Avenue, Washington, DC 20500.”
(Note that DC, like all other abbreviations consisting of two or more uppercase letters, requires no punctuation. Also, all the letters in ZIP, an acronym for “Zone Improvement Plan,” should be capitalized.)
When should you list a state or nation in addition to the name of a city, and which cities are familiar enough that their location does not need to be further specified? The distinction is arbitrary and based on context: A local newspaper need not identify the state in which an obscure nearby town is located, but a publication with national distribution should provide more information about the community’s location; the approach for a book depends on whether the setting is local or the text refers to a variety of locales.
Companies and organizations that regularly publish content featuring references to geographic locations should establish, as part of a style guide, a list of names of cities that stand on their own and those that should be accompanied by the name of a state or nation.
2. Month-Day-and-Year References
In a month-day-and-year phrase, set the year off between commas: “Children born on February 29, 2012, will have to wait four years for their next birthday party.” If only the month and year are used, no punctuation is necessary: “Precipitation levels in April 2012 were nearly double those recorded last year during that month.” The same rule applies for holidays with years: “The caption identified the occasion as Christmas Day 2012.” No punctuation is used in the day-month-year system: “The next sample will be collected on 1 May 2012.”
3. Generational Suffixes
Though those who append Jr. or Sr. (Jnr. or Snr. in British English) to their name may choose to use one or two commas (depending on whether the designation is at the end of a sentence or in its midst) to set the element off, this style is outdated and seldom applied anymore. For the sake of consistency, always omit such punctuation. Also, this usage is not, and never has been, correct in association with II, III, and the like to denote use of an identical name down through successive generations.
4. Legal Endings
Likewise, Inc., Ltd., and other designations of corporate structure are variously treated according to a particular company’s preference, but the dictates of consistency overrule such choices. Of course, if you work for a company that deliberately sets the element off with punctuation, follow that style, but the importance of consistency necessitates that in your employers’ publications or documents, you refer to any other company according to the same rule even if the other company omits punctuation in its treatment of its name. (But what if that other company is a strategic partner, and you feel the urge to honor its style? Resist — I won’t tell if you don’t tell.)