Should individual letters be preceded with "an"?

Question

I was reading a comic book and I noticed that the author used "an A" and "an N" in a particular phrase (screenshot below). While I understand the usage of "An A" here (A being a vowel and what not) and "N" having a pronunciation which has a sound similar to "A".

Since most of English alphabets have pronunciations which start with a syllable similar to one of the vowels or semi-vowels; is it OK to prefix the letters using "An"?

For eg. An X, or An Y.

_{Zenescope's Grimm Fairy Tales - Werewolves: The Hunger, page #8 (Click to enlarge)}

Answer 1

The a/an rule is based solely on pronunciation, not the actual letter that follows.

So it's…

• An eye for an eye
• An LSD drug user

But note:

• An honorable death
• An honest answer
• but… A human reaction

(don't get me started on an hotel)

So, yes… your example would be written out:

… an 'A'.

Answer 2

Robert Cartaino and kiamlaluno have answered your question, but since there are only twenty-six letters, I thought I'd try to illustrate the point by typing up a pair of lists.

The following letters begin with vowel sounds:

an A
an E
an F
an H
an I
an L
an M
an N
an O
an R
an S
an X

The following letters do not:

a B
a C
a D
a G
a J
a K
a P
a Q
a T
a U
a V
a W
a Y
a Z

(I believe the letter H has a variant pronunciation, but I'm ignoring that in these lists.)

As you can see, "most" is inaccurate here. Roughly half of the letters have names beginning with vowels.

Answer 3

You use an for words starting with vowel sounds, and a for words starting with a consonant sound.

So, it's:

• An X (/eks/)
• A U (/juː/)
• A NASA employee (NASA is pronounced /ˈnæsə/)
• An FM radio (FM is pronounced /ef em/)

Answer 4

Taking a cue from @snailplane, I thought I would spell out the names and pronunciations (in IPA) of all the letters of the English alphabet.

Letters beginning with a vowel sound, and so would preceded by an:

an A, the letter a, pronounced /eɪ/, beginning with the vowel /eɪ/
an E, the letter e, pronounced /iː/, beginning with the vowel /iː/
an F, the letter ef, pronounced /ɛf/, beginning with the vowel /ɛ/
an H, the letter aitch, pronounced /eɪtʃ/, beginning with the vowel /eɪ/
an I, the letter i, pronounced /aɪ/, beginning with the vowel /aɪ/
an L, the letter el, pronounced /ɛl/, beginning with the vowel /ɛ/
an M, the letter em, pronounced /ɛm/, beginning with the vowel /ɛ/
an N, the letter en, pronounced /ɛn/, beginning with the vowel /ɛ/
an O, the letter o, pronounced /oʊ/, beginning with the vowel /oʊ/
an R, the letter ar, pronounced /ɑr/, beginning with the vowel /ɑ/
an S, the letter ess, pronounced /ɛs/, beginning with the vowel /ɛ/
an X, the letter ex, pronounced /ɛks/, beginning with the vowel /ɛ/

Letters beginning with a consonant sound, and so would preceded by a:

a B, the letter bee, pronounced /biː/, beginning with the consonant /b/
a C, the letter cee, pronounced /siː/, beginning with the consonant /c/
a D, the letter dee, pronounced /diː/, beginning with the consonant /d/
a G, the letter gee, pronounced /dʒiː/, beginning with the consonant /dʒ/
a J, the letter jay, pronounced /dʒeɪ/, beginning with the consonant /dʒ/
a K, the letter kay, pronounced /keɪ/, beginning with the consonant /k/
a P, the letter pee, pronounced /piː/, beginning with the consonant /p/
a Q, the letter cue, pronounced /kjuː/, beginning with the consonant /k/
a T, the letter tee, pronounced /tiː/, beginning with the consonant /t/
a U, the letter u, pronounced /juː/, beginning with the consonant /j/
a V, the letter vee, pronounced /viː/, beginning with the consonant /v/
a W, the letter double-u, pronounced /ˈdʌbəljuː/, beginning with the consonant /d/
a Y, the letter wye, pronounced /waɪ/, beginning with the consonant /w/
a Z, the letter zee, pronounced /ziː/, beginning with the consonant /z/