Se forma el negativo del verbo ‘to be’ colocando ‘not’ inmediatamente después del verbo. Por ejemplo:
Mario is an engineer
Mario is not an engineer.
Frank and Jenny are pilots
Frank and Jenny are not pilots.
he is --- he’s
she is ---- she’s
we are –we’re
Singular
Si queremos abreviar “is not”
1) is not ---- isn’t : He isn’t a teacher.
Si queremos abreviar “He is”
2) He is not ---- He's : He's not a teacher.
Plural
Si queremos abreviar “are not”
1)are not ---- aren’t: They aren’t students
Si queremos abreviar “They are”
2) They are : They’re : They’re not students