Peter was a clever boy. On his first day at school, he learned three words: I, You and She. The teacher taught him how to make sentences with those words. The teacher said, I, I am your teacher; (then pointing to a girl) She, She is your classmate; You, You are my student.

When Peter went home, his father asked him what he had learned at school. Peter said at once, I, I am your teacher; (then pointing to his mother) She, She is your classmate; You, You are my student His father got angry and said, I, I am your father; (then pointing to his wife) She, She is your mother; You, You are my son.

The next morning at school, the teacher asked Peter if he had learned the three words by heart. Yes, he said proudly, I, I am your father; (then pointing to a girl) She, She is your mother; You, You are my son.