Is it "using an MD simulation" or "using a MD simulation"? MD stands for "Molecular Dynamics".

Since "M" is pronounced "EM", I thought it must be "an". I found both usages on the web through searching in Google.

1 Answer 1


It is one of the extremely rare universal rules of English: the indefinite article an is used with words that begin with vowel sounds, and a with words that begin with consonant sounds. Note that this is a pronunciation rule, not a spelling rule, thus

  • a uterus
  • an utterance

As a consequence, the expected article may differ depending on region or dialect.

  • a herb garden (most British speakers)
  • an herb garden (most American speakers)

Whether a MD or an MD is appropriate therefore depends on how MD is to be pronounced. If it is an initialism, em dee, then an MD is correct. If it is an abbreviation meant to be read out in its long form, then a MD could be correct, as in a Maryland or a medical doctor.

Sometimes, there is no agreement on how to pronounce a word or abbreviation, and both variants can be found in use:

  • a SQL query (a sequel query)
  • an SQL query (an ess-queue-ell query)
  • +1 for a good explanation of the rules, but I think your last sentence is incorrect. The question clearly states that the intended pronunciation in this context is "em-dee". Commented Jan 23, 2017 at 15:13
  • 1
    At first read, I thought a Maryland sounded pretty near nonsensical, but, after I thought more about it, I realized Maryland could be used adjectively in a phrase like "a Maryland state trooper" or "a Maryland state legislator". (The SQL example is excellent, btw.)
    – J.R.
    Commented Jan 23, 2017 at 15:51
  • i would say just try to pronunciate and then choose the one you feel natural.
    Commented May 6, 2020 at 14:02
  • @AlphaDraconis The question states that, but it is unsupported: isn't the truth that when you see "MD simulation", you have no way of knowing whether the author intended you to say "em-dee simulation" or "molecular dynamics simulation"? Actually, perhaps you do have a way: if the author has written "a" then logically they must intend you to speak out the item in full as "molecular dynamics". But this logic relies on everyone knowing and following the rules.
    – rjpond
    Commented Sep 10, 2021 at 7:38

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