Question on indefinite article (Part 2)

when it comes to an English, article really trips me up so I ask another question regarding article(definite/indefinite).
I was studying English grammar and ran into below sentence:

"Make sure the indefinite pronouns and verbs agree in number"

hmmmmm number.. is a noun.. and it's countable(????)

I expected this to be "in a number".
Shall I think that because pronouns and verbs are plural, this is describing more than 1? and there for no article was used?

Based on assumption, is below statement correct?

"Make sure the indefinite pronoun and verb agree in a number" ?

Also, can someone please recommend some site or grammar book best suited to describe all this? (Most grammar book that I saw does not go deep into article(complex case)).
Also, do typical native english speaker know noun is countable vs none countable in real live dialog? I don't understand how this works.

Many thanks in advance!

Answer

It's easy to get tripped up with definite and indefinite articles.

In this case the word "number" is a linguistic term, or a characteristic or a property of something. If you use the word "color" or "beauty" as generic properties in the same way you might say:

• "Make sure the door and the wall agree in color." or


• "Make sure the house and garden are alike in beauty."


• "The rhinoceros and the lion are similar in ferocity."

You would not say "in a color" or "in a beauty" or "in a ferocity".

In the matter of "number" (i.e. is it plural or singular), you are also dealing with a characteristic or property, and not a concrete object.