I am assisting a Hebrew speaker in improving her skills in English. She is having a difficult time understanding how English speakers use the S, and I am looking for the simplest way to explain this. For example, the following phrases seem inconsistent to her: It sounds right. VS. It doesn't sound right. If you can help me help her, it would be appreciated.
It is extremely easy: the s or es is only ever in the third person singular of a verb in the present tense, except the verb be.
Third person is: It/He/She.
Structure of types of sentences:
Declarative: It sounds right.
Negative: It does not sound right. [doesn't]
Interrogative: Does it sound right?
It follows the rule except you have to know how to form a question with the helping verb do. Do in the third person is does. There's your es.
Please note: there are other verbs that take ES in the third person in the declarative form: to slouch, slouches//to mooch, mooches//to finish, finishes etc.
Most though just take an s.
That is basically the only rule about any change to the verb form. English does not have "conjugations" except the one I just gave. It's call a third-person morpheme. Often, learners will forget "Does[subject or pronoun] [verb] and that is a bad mistake.
What is important, however, is the structure of the negative and interrogative. Also, once you learn that the structure of other tenses follows the same pattern of inversion with the helping verb (do).