Proper nouns always begin with a capital letter. Like common nouns, they refer to persons, places or things, but proper nouns specify a person or thing's official or formal name, if it has one. For example, the word "country" is a common noun, but "America" is a proper noun. Proper and common nouns share some overlap when it comes to pluralization, but the rules for pluralizing proper nouns include some exceptions.

Standard Spelling

The most common way to pluralize a proper noun entails simply adding an "s" at the end. Add "s" to the end of "America" to make "Americas." This refers to the North and South continents of America together. Brand name products simply take an "s" ending as well, such as in "iPads" or "Hondas." First names and surnames pluralize by adding "s" too: "There were three Jennifers and two Smiths in the class."

Ending in S, Ch, Sh, Z or X

When any noun, whether common or proper, ends in "s," "ch," "sh," "z" or "x," pluralizing with simply an "s" sounds awkward. In these cases, add "es" to proper nouns, just like with common ones. "Thomas" becomes "Thomases," "Mitch" becomes "Mitches," "Fox" becomes "Foxes" and so on.

Abbreviations

Sometimes proper nouns take an abbreviated form. For example, "United States of America" becomes "USA." The same rules for pluralizing nouns apply to abbreviations: just add "s," unless the abbreviation ends in "s," "ch," "sh," "z," or "x." Thus, the plural form of "USA" becomes "USAs" and "UPS" (United Postal Service) becomes "UPSes." In the cases of titles after names, write either "the Robert Kline Jrs." or "the Robert Klines Jr." Use the latter for more formal situations.

Exceptions

Some exceptions apply to proper noun pluralization. Usually, changing a word ending in "y" that is preceded by a consonant to "ies" applies only for common nouns. So we write "bunnies" and "Fannys." However, sometimes the proper names of mountain ranges take an "ies" pluralization, such as in "Rockies" and "Alleghenies." Another rare exception entails when a proper noun already ends in "s" or "es" and would sound too awkward adding another "es" to pluralize it. In this case, writers should simply leave it as is, such as in "Hastings" or "Hodges."