Page 2 - CFEM_TD2LOE_ingles_unit5

PRESENT CAN or AM ABLE TO
PAST COULD or WAS ABLE TO
FUTURE WILL BE ABLE TO

BE ABLE TO is used in all tenses

MUST, HAVE TO:

Positive and Negative

They have similar meaning in the positive:

You must leave (meaning you can´t stay)

You have to leave (meaning you can´t stay)

They have a different meaning in the negative:

You mustn´t leave (meaning obligation, you can´t go)

You don´t have to leave (no obligation, you can go or stay, as you like)

HAVE TO is not a modal verb, but it is mentioned here because it often has the same meaning
as MUST.

SHOULD, OUGHT TO

They have similar meanings. OUGHT TO always uses TO, SHOULD never uses TO:

Should we go?

Ought we to go?

You shouldn´t make a noise in here

You oughtn´t to make a noise in here

SHOULD, OUGHT TO, MUST, HAVE TO

1. Advise or recommendation: SHOULD and OUGHT TO have similar meanings
a. You should tell your father about this problem
b. You ought to tell your father about this problem
2. Indicating a probable future event: SHOULD and OUGHT TO have similar meanings:
a. They should be here soon
b. They ought to be here soon
3. In reported speech, SHOULD is used instead of SHALL
a. I asked if I should open the door
4. MUST and HAVE TO have similar meanings in the positive, but MUST is sometimes
used to show a position of authority