Indefinite Article Use with Abbreviations

Although proper article usage is generally a challenging aspect of writing in English, deciding which indefinite article to use (a or an) is relatively straightforward. As outlined in another article, a is used when a noun or adjective begins with a consonant sound, whereas an is implemented before a vowel sound. Consonants are often pronounced like consonants, and vowels are usually pronounced like vowels, with some exceptions. For example, in American English, H sounds like a consonant in “a hundred” but sounds like the vowel O in “an hour,” and U sounds like the consonant Y in “a university” but sounds like a vowel “an undergraduate.”

Choosing whether to use a or an with an abbreviation or acronym may be more complicated. If an abbreviation is typically spoken letter by letter, the indefinite article should be chosen according to the pronunciation of the first letter itself, rather than of the actual phrase represented by the abbreviation. A useful trick that you can use to determine whether a letter presents a consonant or vowel sound is to use transliteration or to read aloud. For example:

• A Food and Drug Administration-approved polymer
• An FDA-approved polymer

Unlike “Food and Drug Administration,” which begins with the consonant sound “f,” “FDA” is pronounced “eff-dee-ay” and thus begins with an E-like vowel sound. Therefore, the indefinite article an precedes the acronym “FDA.” In addition to the letter F (“eff”), other letters that are preceded by the article an when read individually are the vowels A (“ay”), E (“ee”), I (“eye”), and O (“oh”) and the consonants H (“aych”), L (“el”), M (“em”), N (“en”), R (“ar”), S (“ess”), and X (“ex”), which are all vowel sounds.

The rules for indefinite article use are different if an abbreviation is commonly pronounced as a word, and not as a series of letters. For example, “FACS,” which stands for “fluorescence-activated cell sorting,” is typically pronounced “fax,” and not “eff-ay-cee-ess.” Therefore,

• A fluorescence-activated cell sorting analysis
• A FACS analysis

Indefinite article use with other acronyms and abbreviations may be confusing if pronunciation varies in the field. One example is “miRNA,” an abbreviation for “microRNA,” which in turn is an abbreviation for “micro-ribonucleic acid.” The term “miRNA” is alternately pronounced as “em-eye-RNA,” “microRNA,” or “my-RNA,” seeming to necessitate an, a, and a, respectively. How can we determine the correct indefinite article to use in this case? A quick Google Scholar search reveals that “a miRNA” yields 18,000 hits, whereas “an miRNA” results in only about 5,000, indicating that the more typical choice of article with “miRNA” is a. Generally, if you are unsure about which indefinite article to use with a particular abbreviation, a review of specific literature in your field and conversations with colleagues may also be useful.

We hope that today's editing tip has clarified the nuances of indefinite article use with abbreviations. Please email us with any comments or questions.