MODALS OF DEDUCTION: MUST, CAN´T, MIGHT/ MAY/COULD

Los verbos modales son verbos auxiliares que no pueden funcionar como un verbo principal, a diferencia de los verbos auxiliares “be”, “do” y “have” que sí pueden funcionar como un verbo principal.
Los verbos modales expresan modalidad, habilidad, posibilidad, necesidad u otra condición. Los utilizamos para el futuro y el condicional.
Como verbos complementarios que son, los verbos modales no funcionan sin otro verbo. Este otro verbo siempre va después del verbo modal y está en la forma base (el infinitivo sin “to”). No se conjugan los verbos modales y no tienen tiempo.

Los verbos modales son:

Must

Cant´t

Might/May/Could

Some modal verbs can be used to express probability in the present and past.

Must, can't: expressing present probability
Structure: modal + verb infinitive without ‘to’ must be, can’t be, must have, can’t have, etc.
We use must to express that we feel sure that something is true.	The team is playing really well today; they must win. They must be very rich – look at their big house!
We use can't to say we are sure that something is impossible.	She can't be so ill – I saw her playing volley ball yesterday. I don't believe you – it can't be true.

May, might, could: probability in the present
Structure: modal verb + verb infinitive without ‘to’ may be, might do, could go, etc.
We use may, could or might to say that it is possible that something will happen in the future or is happening now.	They may be arriving tomorrow. He might be away on holiday at the moment. He could be away on holiday. He might get the job.
The negative of may is may not. The negative of might is might not. Both may not and might not mean that it is possible that something will not happen or is not happening now.	He might not get the job. I may not pass the exam. I might not go to the match tomorrow.

Could

“Could” indica posibilidad o habilidad en el pasado.

Ejemplos:

Joe could speak Spanish when he was young.(Joe podía hablar español cuando era joven.)
I couldn’t sleep last night.(No pude dormir anoche.)
Could you play an instrument when you were a child?(¿Podías tocar un instrumento cuando eras un niño?)

May

Como “could”, se usa “may” para indicar posibilidades en el futuro.

Ejemplos:

I would bring an umbrella, it may rain later.(Llevaría un paraguas, puede llover más tarde.)

It may be better to finish this now, rather than wait until tomorrow.(Tal vez sea mejor terminar esto ahora, en lugar de esperar hasta mañana.)

Might

Se usa “might” para indicar posibilidades en el presente o el futuro. En estos casos, es un sinónimo de “may”.

Ejemplos:

I would bring an umbrella, it might rain later.(Yo llevaría un paraguas, puede llover más tarde.)

It might be better to finish this now, rather than wait until tomorrow.(Tal vez sea mejor terminar esto ahora, en lugar de esperar hasta mañana.)

Forma negativa:

En un juicio sobre la probabilidad, la forma negativa de must es can’t – es imposibile que algo ocurra:

He can’t be ill. I saw him this morning jogging in the park. (No puede estar enfermo)