Acronyms and initialisms
According to The Business Writer's Handbook, "An acronym is an abbreviation that is formed by combining the first letter or letters of several words. Acronyms are pronounced as words and are written without periods.
EXAMPLES: radio detecting and ranging/radar Common Business-Oriented Language/ COBOL self-contained underwater breathing apparatus/ scuba
An initialism is an abbreviation that is formed by combining the initial letter of each word in a multiword term. Initialisms are pronounced as separate letters.
EXAMPLES: end of month/ e.o.m. cash on delivery/ c.o.d. post meridian/ p.m.
The following are sample guidelines to apply in deciding whether to use acronyms and initialisms:
--If you must use a multiword term as much as once each paragraph, you should instead use its acronym or initialism. For example, a phrase such as "primary software overlay area" can become tiresome if repeated again and again in one piece of writing; it would be better, therefore, to use PSOA.
--If something is better known by its acronym or initialism than by its formal term, you should use the abbreviated form. The initialism a.m., for example, is much more common than the formal ante meridiem. If these conditions do not exist, however, always spell out the full term.
--The first time an acronym or initialism appears in a written work, write the complete term, followed by the abbreviated form in parentheses.
EXAMPLE: "The Capital Appropriations Request (CAR) controls the spending of money." Thereafter, you may use the acronym or initialism alone. In a long document, however, you will help the reader greatly by repeating the full term in parentheses at regular intervals so that he or she does not have to search back to the first time the acronym or initialism was used to find its meaning.
EXAMPLE: "Remember that the CAR ( Capital Appropriations Request ) controls the spending of money."
Write acronyms in capital letters without periods. The only exceptions are those acronyms that have become accepted as common nouns, which are written in lowercase letters.
EXAMPLE: "NASA," "HUD," "laser," "scuba." Initialisms may be written either uppercase or lowercase. Generally, do not use periods when they are uppercase, but use periods when they are lowercase. Two exceptions are geographic names and academic degrees.
EXAMPLES: EDP/e.d.p., EOM/e.o.m., OD/ o.d." (14-17).
Plurals of words, acronyms, and initialisms not normally pluralized?
Form the plural of an acronym or initialism by adding an s. Do not use an apostrophe.
EXAMPLES: "MIRVs," "CRTs." To form the plural of words that do not have true plural forms, just add s.
EXAMPLES: "The dos and don'ts of writing are many." "The ifs, ands, or buts of life are many."
A or An?
According to The Oxford Dictionary of American Usage and Style, "The indefinite article a is used before words beginning with a consonant sound, including /y/ and /w/ sounds. The other form, an, is used before words beginning with a vowel sound. Hence, a European country, a Ouija board, a uniform, an FBI agent, an MBA degree, an SEC filing. Writers on usage formerly disputed whether the correct article is a or an with historian, historic, and a few other words. The traditional rule is that if the h- is sounded, a is the proper form. Most people following that rule would say a historian and a historic--e.g.:'Democrat Bill Clinton appears within reach of capturing the White House in Tuesday's election, but Republicans hope that late momentum, can enable President Bush to win a historic upset' (Dallas Morning News). Even H.W. Fowler, in the England of 1926, advocated a before historic(al) and humble (MEU1).
The theory behind using an in such a context, however, is that the h- is very weak when the accent is on the second rather than the first syllable (giving rise, by analogy, to an habitual offender, an humanitarian, an hallucinatory image, and an harassed schoolteacher). Thus no authority countenances an history[emphasis added], though a few older ones prefer an historian and an historical.
Today, however, an hypothesis and an historical are likely to strike readers and listeners as affectations. As Mark Twain once wrote, referring to humble, heroic, and historical: 'Correct writers of the American language do not put an before those words' (The Stolen White Elephant,1882). Anyone who sounds the h- in such words should avoid pretense and use a (Garner 1).