I'm trying to determine the plural form of the scientific term "Mechanism of Action". I'm pretty sure the answer is, "Mechanisms of Action", but the term "Mechanisms of Actions" is disturbingly popular.

Do a google search for "Mechanisms of Actions", and I get 336,000 results, compared to what I think is the correct spelling (no 's' at the end of "Action"), which gets some 21,000,000 results.

So which is right?

  • Those are two commonly used phrases which have different meanings and are both correct in their own respects. It is a simple question of how many actions there are. What is increasing? The mechanisms, the actions, or both? – Alex W Aug 19 '15 at 18:50
  • Google search counts are extremely unreliable. Google Ngrams are a much better indication. This one shows "mechanism of actions" is extremely infrequent compared to "mechanisms of action". – Peter Shor Aug 19 '15 at 18:51
  • In virtually all cases it would be "mechanisms of action". There may be some contexts where "... actions" is a better choice, but I'm not thinking of one right now. – Hot Licks Aug 20 '15 at 12:40

Google hit counts are extremely unreliable. Even if you know they are unreliable, and you think you are taking this into account, you will occasionally run across searches in which they are orders of magnitude more unreliable than you ever thought they could be. I believe you've just discovered one of them.

Google Ngrams are a much better tool for deciding how frequent phrases are. The linked one shows that "mechanisms of actions" occurs at roughly 2% the frequency of "mechanisms of action". For scientific literature, where there are many authors who do not have a good grasp of English, I think this is a fairly low error rate.


How many actions are you referring to?

"Mechanisms of action" says there are many mechanisms producing one action.

"Mechanisms of actions" says there are many mechanisms, and many actions.

I would use the one that matches up to what you're writing about.

  • In my case, I'm referring to a single drug (or more broadly, a compound), which has many different mechanisms of action(s?). Think of it like this: there is a list of several entities, and each entity is a single mechanism of action. – DJohnson Aug 19 '15 at 18:55
  • @DJohnson: in mechanisms of action, I perceive the word action as an uncountable noun which should never be pluralized. – Peter Shor Aug 19 '15 at 19:01
  • @Zwi Could you please provide me with at least one authoritative source that uses that uses "Mechanisms of Actions"? I don't mean to disagree with you, but the only usages I can find at first glance are articles in scientific journals...and perhaps counter-intuitively I don't consider them to be credible sources of correct English usage. – DJohnson Aug 19 '15 at 19:01
  • I would lean towards using "mechanisms of action". But the assumption I make is that one drug is supposed to have one main effect, but maybe there's multiple compounds contributing to that effect. Even if it has other effects, such as side-effects, I'd assume the drug has one main goal, or effect that is wanted, so I'd lean towards the word choice that highlights that. This all said, I'm not an expert in pharmaceuticals , and would look at Peter Shor's answer as it's more supported. – Zwi Aug 19 '15 at 19:03

MIT has a course called Mechanisms of Drug Actions.

  • Hello, MDavis, and welcome to English Language & Usage. Your answer provides an instance of the use of "Mechanisms of ... Actions," but it doesn't attempt to answer the core question asked above: which form—"Mechanisms of Action" or "Mechanisms of Actions"—is correct? Please consider revising your answer to address that question. – Sven Yargs Aug 20 '15 at 7:27

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