Opinions vary regarding the use of apostrophes when forming the plurals of letters of the alphabet.New Fowler's Modern English Usage, after noting that the usage has changed, states on page 602 that "after letters an apostrophe is obligatory." The 15th edition ofThe Chicago Manual of Style states in paragraph 7.16, "To avoid confusion, lowercase letters ... form the plural with an apostrophe and an s". TheOxford Style Manual on page 116 advocates the use of common sense.
