«must» usado para la deducción

[A] Formas

PRESENTE:

must + infinitivo de presente: He must live here, o bien

must + infinitivo continuo: He must be living here. 

PASADO:

must + infinitivo de perfecto: He must have lived here, o bien

must + infinitivo de perfecto continuo: He must have been living here.

Notar la diferencia entre las formas de pasado de must usado para la deducción y el pasado equivalente de must usado para la obligación: had to.

must no se emplea para la deducción negativa y tampoco se usa en oraciones interrogativas excepto si se cuestiona una deducción con must:

• There’s a lot of noise from upstairs. It must be Tom. – Why must it be Tom? Other people use that flat.  

[B] Ejemplos

• He has a house in London and another in Paris, so he must be rich.
• I’ve had no sleep for 48 hours. – You must be exhausted.
• He develops his own films. That must save him a lot of money. 
• I keep meeting him on the bus. He must live/must be living near by.
• The police are stopping all cars. They must be looking for the escaped prisoner. 
• What explosion? I didn’t hear any. – You must have heard it! The whole town heard it.
• He must have taken sleeping pills last night. He didn’t wake up till luch time.
• I waited under the clock! – So did I, but I didn’t see you! We must have been waiting under different clocks.
• It was a head-on collision, but the drivers weren’t hurt. – They must have been wearing their seat belts.