How can you decide whether the verb is singular or plural?

1. You can decide whether a verb is singular or plural usually if it ends with letter 's'

2. If it precedes a singular or plural noun or pronoun ( where the sentence subject is direct).

e.g. GO (plural) GOES(singular)

The Boy is big ('is' after 'The boy' singular)

The boys are big ('are' after 'The boys' plural).

Some verbs are irregular and the singular form is not verb + s but is a new Word eg do-does, go-goes, have-has.