Use "a" before words that begin with a consonant sound, and "an" before words that begin with a vowel sound.
Use "a" before words that begin with a consonant sound.
I need to buy a notebook.
I need to buy an notebook.
Use "an" before words that begin with a vowel sound.
There's an orange on the table.
There's a orange on the table.
Note that this rule is based on pronunciation, and not spelling. For example, the first letter of the word "European" is a vowel, but it has a consonant sound (a "you" sound). Therefore, it takes the indefinite article "a" (not "an").
My wife is a European citizen.
Other words, such as "hour" or "honor", begin with a consonant; however, since the "h" is silent, we use "a" because the initial sound of these nouns is not consonant.
It's an honor to be your guest.
Follow the same convention to introduce a single letter in a sentence; for example, we say "an F" because the individual letter "F" starts with a vowel sound (similar to "eff").
Yesterday a bought an expensive necklace with an F on it.
And we say "a U" since this letter is pronounced with a consonant sound ("you").
It's a U-shaped statistical curve.
A partial list of words and acronyms that begin with a consonant but take the article "an", and vice versa, can be found below.
List of Special Words With a/an
As mentioned before, we say "a U" (not "an U"). By contrast, when pronouncing the following consonants as individual letters, we use the indefinite article "an" to say:
Words Beginning With EU
Despite beginning with a vowel, the following words start with a consonant sound (a "you" sound), and therefore they take the article "a":
Words Beginning With F
Follow the same strategy with abbreviations that begin with F and are pronounced as individual letters; for example, we say:
Words Beginning With H
These words begin with a vowel sound because the initial letter H is silent. Consequently, they take "an":
- an heir
- an heiress
- an heirloom
- an herb (American English)
- an herbal (American English)
- an honest
- an honor
- an honorable
- an honorarium
- an honorary
- an hour
- an hourly
- an hourglass
When pronounced as individual letters, these acronyms begin with a vowel sound and are preceded by the article "an" as well:
- an HDL (High-Density Lipoprotein)
- an HDD (Hard Disk Drive)
- an HDMI (High-Definition Multimedia Interface)
- an HIV (Human Immunodeficiency Virus)
- an HPV (Human Papilloma Virus)
- an HTML (HyperText Markup Language)
- an HTTP (HyperText Transfer Protocol)
By contrast, these words begin with a sounded "H" (a consonant sound), so we use the article "a":
- a habit
- a helicopter
- a hardware
- a historic
- a historical
- a hospital
- a host
- a hostess
- a hotel
- a humble
- a hypothesis
Some English words starting with H, like the ones listed below, can be pronounced in two different ways (either with a silent H or a sounded H). In such a situation, choose the article (a/an) that best suits your own pronunciation:
Words Beginning With L
These abbreviations are typically pronounced as individual letters, and therefore take the article "an".
- an LDL (Low-Density Lipoprotein)
- an LGB (Lesbian, Gay, Bisexual) & LGBT (Lesbian, Gay, Bi, Transgender)
Words Beginning With M
Despite starting with the consonant M, these acronyms are often pronounced as individual letters and take the article "an":
- an MBA (Master of Business Administration)
- an MD (Doctor of Medicine)
- an MIT (Massachusetts Institute of Technology)
- an MRT (Mass Rapid Transit)
These abbreviations, by contrast, are commonly pronounced as words (milliliter and millimeter) and are usually preceded by a:
Words Beginning With N
Use an before acronyms that begin with N but are pronounced as individual letters; for example, we say:
- an NBA (National Basketball Association)
- an NFL (National Football League)
- an NFT (Non-Fungible Token)
- an NGO (Non-Governmental Organization)
- an NLP (Natural Language Processing)
- an NRA (National Rifle Association)
- an NSA (U.S. National Security Agency)
- an NYSE (New York Stock Exchange)
The Word 'One'
Note that the word one begins with a “w” sound. Actually, many native speakers pronounce “one” and “won” in the same way. Therefore, we say and write “a one” (not "an one").
Robert rolled the die and got a one.
Robert rolled the die and got an one.
Words Beginning With R
Use an before acronyms that begin with R and are pronounced as individual letters, so we say:
But use a if the abbreviation is pronounced as a word and begins with a consonant sound:
Words Beginning With S
Because the following acronyms are usually pronounced as individual letters, and the consonant "S" starts with a vowel sound ("ess"), we use "an" to say:
- an SEO (Search Engine Optimization)
- an SLA (Service-Level Agreement)
- an SMS (Short Message Service)
- an SMTP (Simple Mail Transfer Protocol)
- an SSD (Solid-State Drive)
- an STD (Sexually Transmitted Disease)
- an SUV (Sport Utility Vehicle)
- an SVG (Scalable Vector Graphics)
Words Beginning With U
The following words begin with a consonant sound ("you"), and consequently require the indefinite article "a"
- a unicorn
- a unification
- a unified
- a unifying
- a union
- a unique
- a unit
- a united
- a United Kingdom
- a United Nations
- a United States
- a unity
- a universal
- a university
- a Uruguayan
- a US
- a useful
- a useless
- a user
- a uvula
Follow the same practice with these abbreviations:
- a UFO (Unidentified Flying Object)
- a UID (Unique Identifier)
- a UK (United Kingdom)
- a UN (United Nations)
- a UNESCO (United Nations Educational, Scientific and Cultural Organization)
- a URL (Uniform Resource Locator)
- a US/USA (United States)
Words Beginning With X
Since the pronunciation of the individual letter "X" starts with a vowel sound, use the indefinite article "an" before these abbreviations: