What is the proper way to pluralize acronyms ending in the letter 'S'?

The particular acronym under study in this case is T.A.R.D.I.S.

The various forms I believe are correct are:

  • TARDISes
  • T.A.R.D.I.S.es (is it even correct to pluralize this)

Whoniverse.net and Wikipedia both use TARDISes. This follows general pluralization rules and seems to generalize to pluralizing other acronyms, e.g. radars and lasers, as well as to initialisms such as USBs, GPSes.

It seems that keeping the capital letters for acronyms, as opposed to initialisms, is somewhat uncommon, but we have WASPs, for instance.

Not everyone does, but I'm using the distinction that acronyms are pronounced as words and initialisms are instead pronounced as individual letters, as supported by Ben Zimmer in the New York Times Magazine.

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    The BBC and TARDIS Index File also use TARDIS as singular and TARDISes as plural. – Hugo Jan 4 '12 at 14:07
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    @Hugo Good references to support the capitalization. Thanks. – sarah Jan 4 '12 at 22:09
  • @z7sg Ѫ Thanks for the much needed edits. I'm such a crap typist on this particular laptop, but I usually catch such obvious typos--I hope so, anyway. :) I need to sleep more. – sarah Jan 4 '12 at 22:14
  • FWIW the BBC's use of Tardis v. TARDIS appears to alternate at random. – Dave Newton Apr 12 '16 at 12:18

The Guardian style guide says:

Use all capitals if an abbreviation is pronounced as the individual letters: BBC, VAT, etc; if it is an acronym (pronounced as a word) spell out with initial capital, eg Nasa, Nato, unless it can be considered to have entered the language as an everyday word, such as awol, laser and, more recently, asbo, pin number and sim card.

Hence, it wouldn't be T.A.R.D.I.S. or TARDIS, but Tardis, and therefore, pluralised, Tardises.

However, the Guardian style guide is only one guide. Other publications may have different rules, and if nobody is making the rules for you, you can choose your own.

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  • I'd note that US reporting, and NASA itself, refers to NASA as NASA, not Nasa, e.g., nasa.gov/press-release/…. This may be a British-English v. American-English thing, though; BBC also uses Nasa. – Dave Newton Apr 12 '16 at 12:14

The general approach is to derive the plural according to how an abbreviation, acronym etc., is pronounced when read aloud.

If T.A.R.D.I.S. is the usual format in writing so that the alphabets are pronounced separately, then it is not advisable to pluralize it at all. You can circumvent this by such alternatives as instances of T.A.R.D.I.S. or such other constructions.

On the other hand, if TARDIS is the usual way it is written and pronounced like a word, then TARDISes would be acceptable and comprehensible to the average reader.

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