From general Googling, I understand it is correct to add an 's' (lower case) if pluralising abbreviations ending in 'S' and this makes sense. However, I am surprised to have so far found no instances of this having been done with the word microelectromechanical systems, which always appears as MEMS (rather than MEMSs).

One on which I find myself truly stuck is power electronics, machines and drives. Again, the abbreviation is always PEMD. However, since it contains several plurals, is a single lower-case s on the end correct?

Any help regarding this would be much appreciated. I am beginning to wonder whether it makes sense to use singular abbreviations regardless. Obviously, one needs to be consistent.

  • 1
    It seems to me that in these cases the abbreviation itself is already plural. So pluralising it by adding an "s" does not make sense. It would be like saying "microelectromechanical systemses". (Of course you can wonder why MEMS is not the abbreviation for a singular system, but apparently by convention it isn't.)
    – towr
    Commented May 29, 2022 at 14:46
  • Thanks for your reply, but one might refer to a 'microelectromechanical system device' or say something along the lines of 'a microelectromechanical system is a miniature machine that has mechanical and electronic components', so my thinking was that singular and plural abbreviations are needed.
    – Liza
    Commented May 29, 2022 at 21:57
  • English writing is not a good representation of English pronunciation or grammar. In fact, plural marking and agreement is not particularly important in English, and in a situation where letters are being deleted, irrelevant morphology is the first to go. I.e, don't bother with plurals in abbreviations. Commented Jun 2, 2022 at 13:29
  • grammar questions are off-topic here writing.stackexchange.com/help/on-topic
    – levininja
    Commented Jun 14, 2022 at 14:33
  • It's common to talk about LEDs, GIFs, or JPEGs, for instance. Maybe MEMS already sounds plural. Or a mass noun like CMOS. Unsure about GPSes but it seems possible.
    – Stuart F
    Commented Jun 14, 2022 at 17:26

1 Answer 1


In my version of The Chicago Manual of Style (14th ed.), the relevant guidance (from section 6.16) is:

So far as it can be done without confusion, single or multiple letters . . . form the plural by adding s alone

Several examples follow, including:

all SOSs
several YMCAs and AYHs
CODs and IOUs

However, there is a problem: "SOS", "YMCA", "AYH", "COD", and "IOU" are usually construed as singular, but your description of "PEMD" suggests that it is already plural. If the reader is likely to understand it that way, then you could justify the following:

Several PEMD were used.

If this is unlikely to sound natural to your audience (after all, "PEMD" does not take an obviously plural form), then I recommend rephrasing. For example:

Several PEMD devices were used.

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