Plural or singular verb?

Hi Magda,

Technically, you should use "are" because you have two things there. But it may sound a little off, because the noun that is right next to the verb is singular. To make it both sound correct as well as be correct, you could rewrite: "He doesn't even know what adjectives and adverbs are."

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When two singular subjects are joined by and, the verb is normally plural.

Alice and Bob are going to be late.

Swan, Practical English Usage, singular and plural, coordinated subjects, p. 509
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When two subjects are joined by or, the verb

Thanks, Marius.
I will keep this rule in mind. What I am puzzled by, however, is the fact that either of the examples you gave me doesn't refer exactly to the sentence I gave.
In your first example, we deal with proper names, no articles there, and in the second one, with one noun in plural and the other in singular.
If I kept this rule in my sentence, I should write "He doesn't even

0plural for book02br
02br
00paper02br
02br
00pencil02br
02br
00toy02br
02br
00hat02br
02br
00car 02br
02br
00ring02br
02br
00marker02br
02br
00cupcake02br
02br
00mitten0-

0Add01i00 S.02i0-

0I think the answer to your original question, Magda, is that if you want to keep your original sentence, just change "is" to "are". The thing is, it's an unusual sentence, so Grammar Geek gave you a more common one. I don't think many native English speakers would know with 100% certainty which verb to use in your sentence, probably because it's an unusual construction. But I guess Grammar Geek

I think what might work better would be either:
"He doesn't even know what an adjective or adverb is." This allows you to keep the article an in the sentence.
Or, if you want to take the article an away (which might work better if you mean to emphasize that he doesn't know both), then what might work better would be: "He doesn't even know what adjectives and adverbs