Which one is a correct sentence 'classes has started' or 'classes have started'

Question

When I asked why not the classes has started, one of my friend suggested a correction: "have started"

My question is: which one is correct?

Answer 1

"Classes" is a plural noun. The verb must also take a plural form to agree with the noun.

One class has started.

Two classes have started.

Answer 2

The present simple of the verb have goes like this:

singular
I have
you have
he/she/it has

plural
we have
you have
they have

You will notice that the only case of has is third person singular- he/she/it has.

classes is plural, so the correct verb case is have.