When are letters of the alphabet, appearing in isolation rather than as part of a word, capitalized, and when are they lowercased? When should they be italicized, and when is the normal type, called roman, employed? Here’s a general guide to styling letters.
Letters as Letters
When referring to a letter as an alphabetical character in print or online, style it in italics and use uppercase or lowercase forms as appropriate, as in the examples “Notice how the letter m is cut off so that it almost looks like an n” and “Engraved in the rock was a capital A.”
A roman apostrophe and a roman s are added to indicate a plural form, as in “When you wrote ballot, you included three l’s.” For capital letters, the apostrophe isn’t necessary: “The two Vs look like a W.” However, if plural forms of both uppercase and lowercase letters appear in the same document, for consistency, reconcile the style either way.
Letters employed in lieu of an entire word beginning with that letter to disguise profanity or otherwise avoid the word’s use are capitalized and styled in italics: “The F word” refers to an obscene four-letter word, for example, and “the D word” might appear in a perhaps jocular reference to relationships in which the writer declines to use the word divorce.
In idioms such as “Dot [one’s] i’s and cross [one’s] t’s” — or the humorous inversion “Cross [one’s] i’s and dot [one’s] t’s” — and “Mind [one’s] p’s and q’s,” the letters are traditionally not italicized, despite this custom being an exception to the rules described above; instead, an apostrophe is inserted before the plural s. Other idiomatic usage (for example, “the three Rs” and “to a T”) generally does not call for italicization, either.
Names of Letters
In the unlikely event that a letter needs to be referred to by name, it can be spelled out as indicated in dictionaries. However, the system is difficult to use because not all names of alphabetical characters are spelled intuitively, so they’re difficult to locate for verification: B and letters that rhyme with it are spelled bee, cee, and so on, but others are spelled, for example, aitch, cue, and wye.
When the letters A, B, C, D, and F are used in educational contexts and, by extension, in informal analogous usage, as evaluative marks, they are not italicized. That’s because they refer to the points on the grading scale, not to letters of the alphabet; I’ve italicized them here, though, because I’ve named them as letters: “the letter A,” and so on. (Why is there no E in the grading scale? Apparently, educators were concerned that this letter grade would be misconstrued as representing excellent, as F stands for failure, so although it was originally part of the grading scale, it was eventually omitted.)
An alternative system, often used euphemistically in lower grades, is E, G, F, P, and U (excellent, good, fair, poor, and unsatisfactory). No apostrophe is inserted before the plural s; for example, write “I had hoped to receive more As” or “She earned three Es last semester.”
Letters as Shapes
When letters are used to describe shapes, they are capitalized and styled in roman, as in “C clamp” and “T square.” Letters employed in this way are sometimes treated in sans serif type (one of many typefaces in which letters are made solely of straight lines and curves and lack appendages), but this approach looks awkward.
Music and Rhyme Schemes
In general, letters referring to musical pitches are capitalized in roman type — for example, “This song is in D.” (Technical usage such as references to octaves varies; consult specialized print publications or websites for more information.)
Rhyme schemes, however, are indicated in lowercase italic letters with no letter spaces between characters indicating a set of lines constituting a verse, as in “The poem is written in abba rhyme.”