My understanding is when referring to a type of thing in general we can either use the plural form or a singular with the definite article. For example:

The tomato is a fruit, not a vegetable.


Tomatoes are a fruit, not a vegetable.

But can an indefinite article also be used to make a generic reference? I saw this in Google's definition of "scabies":

A contagious, intensely itchy skin condition caused by a tiny, burrowing mite. Skin condition caused by a burrowing mite.

I found this definition kind of odd, because "mite" as a countable noun means an individual organism that belongs to the mite species. I thought the following would make more sense:

A contagious, intensely itchy skin condition caused by tiny, burrowing mites.

A contagious, intensely itchy skin condition caused by a kind of tiny, burrowing mite.

I am almost certain this question must have been asked, but I can't find any related questions. What are the applicable grammatical rules here? Also are there other examples?

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  • @userr2684291 Hugely helpful!! Thanks! The answer I am seeking seems to be part of that question's premise. I am hoping someone will be more detailed in outlining the rules surrounding singular noun and generic reference. – Eddie Kal Apr 30 '18 at 1:07
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    My pleasure! For a more detailed explanation, read what the author of the answer linked, which is a summary of their work, which is again linked on that website ("a dissertation"). More specifically, part 4 deals with the relevant bits. – userr2684291 Apr 30 '18 at 9:11

It's easiest if you just remember this:

Basically, you don't use a/an with plural nouns at all.

Why? Mostly because when you use a plural noun, you either:

  • mean it as a type or abstractly (no article)

    I like socks on my feet (given anything, if that thing is type=sock, I like it on my feet, but I, for example, might not even have seen a sock today, or be near one at the moment)

    Socks are neat (abstract, I'm talking about attributes of sock)

  • are talking about a group of X such you do not mean "any X"

    I like those socks on my feet (I do not mean any socks, but specifically those socks)

Since the indefinite article has a lot of overlap in meaning with any, it doesn't work when you have a group of something you are talking about (because you no longer mean any X).

If you really mean "any group of X" you have to actually say that, with any X or set of X.

I like a set of socks on my feet.

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