modal verb
Expresiones de Certeza o Imposibilidad:
Pistas: "I am certain that...", "I am sure he didn't...", "It is impossible that...", "There is no doubt that..."
Significado: Exige modales de deducción (must have + participio, can't have + participio) o expresiones de certeza (be bound to).
Expresiones de Probabilidad o Expectativa:
Pistas: "It is probable that...", "People expect him to...", "It was arranged that..."
Significado: Exige estructuras con adjetivos modales (be likely to, be supposed to, be due to).
Expresiones de Acción Innecesaria en Pasado:
Pistas: "It was not necessary to do X, but they did it anyway..."
Significado: Exige la estructura needn't have + participio.