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Infrequently Asked Questions Concerning the Proper Spelling of 'DTD' in its Plural Form

  1. Q: How is the plural of DTD to be spelled?
    A: Thus: DTDs

  2. Q: What would the grammatical form DTD's mean?
    A: DTD's is the singular possessive, not the plural absolute. Example: "This DTD's origin is unknown [ == The origin of this DTD is unknown]." DTD's could also represent a contraction for "DTD is".

  3. Q: Why do so many people spell the plural (incorrectly) as DTD's?
    A: Authorities offer different explanations -- while in general agreement that there is an observable trend toward (gratuitous) usage of apostrophe as a plural marker in many contexts (e.g., "pizza's"; "Nut's for sale"), including some very silly contexts ("He complain's a lot." and "We should wait until it cool's off.") Several possible explanations:

    • Writers may subconsciously feel an analogy to "referenced letters" (as in: "Mind your p's and q's."). This could happen because the character string 'DTDs' is typically pronounced or sub-vocalized as a three-syllable word highlighting the alphabetic letters: "dee-tee-dee(z)". The analogy is wrong, however, failing to distinguish linguistic reference from usage. In the example above, the letters "p" and "q" are are not used but are referenced as letters; hence they would normally be set in italic to signify reference/mention (p's and q's). When we say "be sure to dot your i's and cross your t's" we are not using i and t; we are referencing these letters as alphabetic characters. The phenomenon of "referenced letters," however, is fundamentally irrelevant to the use of 'DTD' in its plural formation: with 'DTDs' we are talking about usage, not reference.
    • Writers feel that the morpheme boundary between the base (i.e., DTD) -- which is not an ordinary "word" --- and the simple plural marker s is not sufficiently accounted for by a letter-case-shift. So they want to "add something" in the orthography to mark the boundary. The apostrophe serves as an added marker in the case of simple contractions (e.g., can't for cannot), so it is pressed into service as a marker here too, even though nothing is actually missing in "DTDs". One should no more write "look at these three DTD's" than one would write (for plural absolute) "look at these three document type definition's".
    • Other explanations: ignorance (mere lack of education), forgetfulness, stupidity, inattentiveness, indifference, perversity, postmodernist arrogance, language terrorism, sloth.
    • Another explanation: the orthographic manifestation of mind fumbling and verbal stumbling is apostrophe-insertion. Speakers who suffer episodes of tang tongueling -- i.e., they falter on the pronunciation of 'DTD', often uttering or stuttering 'D-D-T' instead -- are similarly predisposed to suffering finger twitches at the moment of typing 'DTD' in the plural, generating otiose apostrophe.

  4. Q: Do some abbreviations require 's in the plural form?
    A: Some language usage authorities prescribe or allow apostrophe-s in the formation of a plural for an abbreviation that has more than one period. The Chicago Manual, for example, allows: Ph.D.'s as a plural. Note the irrelevance of this question, however: 'DTD' contains no period, and it is not an "abbreviation" (initialism).

  5. Q: What authorities for English usage clarify the rule for plural formation of abbreviations, initialisms, and acronyms?
    A: See the list below.

  6. Q:Why do some people think 'schema' in the plural is schema's, as in "We are developing XML schema's..." or [2000-01-04] "Schema's are essentially DTD's."?
    A: Probably they have contracted the DTD's illness. In the second example one can guess that the author is seduced into thinking the plural must be (sic!) "Schema's" in order to match "DTD's".

  7. Q: What are some other examples from the English language?
    A: URLs (not URL's); CEOs (not CEO's); IDs (not ID's); POs for "purchase orders" (not PO's); RFCs (not RFC's); FOs for "flow objects" (not FO's); STDs (not STD's); TCs for "Technical Committees" (not TC's); CRs for "Candidate Recommendations" (not CR's). And so forth. The concept is not that difficult, if you concentrate on the problem. See also the examples drawn from the style manuals cited below.

  8. Q: What is the 'Apostrolypse'?
    A: The 'Apostrolypse' is a term for the cataclysmic and final collapse of our planet brought on by the misuse of apostrophe by illiterate people, viz., death by apostrophe. Think of it as worse than nuclear fallout: suffocation of all living organisim's by the relentles's rain of gratuitou's apostrophe's, swelling up as toxic aerial miasma... Variant theory: "Apostroluge," or global destruction by deluge; all air-breathing terrestrial creatures are inundated by waves of apostrophes and die, reminiscent of Noah's flood except that there's no boat.

Excerpts from Style Manuals

The Chicago Manual of Style

"So far as it can be done without confusion, single or multiple letters, hyphenated coinages, and numbers used as nouns (whether spelled out or in numerals) form the plural by adding s alone. [Examples: SOSs, several YMCAs and AYHs, CODs and IOUs, the early 1920s." [14th edition, section 6.16]

MLA [Modern Language Association] Handbook for Writers of Research Papers

" not use them [apostrophes] in the plurals of abbreviations or numbers (PhDs, MAs, VCRs, IRAs, 1990s, SATs in the 700s)." [3rd edition, section 2.2.2]

Turabian 'Manual for Writers'

"Form the plurals of most single and multiple capital letters used as nouns by adding s alone: 'The three Rs are taught at the two YMCAs'. [5th edition, section 3.5]

The Gregg Reference Manual

"Capital letters and abbreviations ending with capital letters are pluralized by adding s alone. [Examples:] three Rs, four Cs, five VIPs, six CPUs, CEOs, IQs, PTAs, YWCAs..." [7th edition, section 623]

European Commission Translation Service. English Style Guide

"3.37 Plurals of abbreviations. Plurals of abbreviations (MEPs, OCTs, SMEs, UFOs, VDUs) do not take an apostrophe."

Indiana University Office of Publications Style Guide


Avoid misusing the apostrophe to form plurals. The only nouns that commonly take an ’s in the plural are (1) abbreviations with more than one period and (2) single letters.

M.B.A.’s, R.N.’s

x’s and y’s

A’s and B’s

Otherwise, acronyms, hyphenated coinages, and numbers used as nouns (either spelled out or as numerals) generally add s (or es) alone to form the plural.

AIs, W-2s, 747s, FAFSAs, 1980s, hi-fis, follow-ups, at sixes and sevens

Apostrophes are never used to form the plural of any proper noun.

The Brands will attend.

not: The Brand’s will attend.

As with any plural noun, though, plural proper nouns do add a single apostrophe (no s) to indicate possession.

The reception will be at the Brands’ home, Bryan House.

[Unofficially] Prepared by Robin Cover for The XML Cover Pages archive. [Updated 2001-01-04 or later]


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