Be able to instead of can
Be able to often has the same meaning as can.
- He can walk on his hands. OR He is able to walk on his hands.
- I am unable to understand his motive. OR I can’t understand his motive.
- They were able to catch the thief. OR They could catch the thief.
Be to instead of will or shall
The structure be + to can be used to express simple futurity.
- He is to retire next year. = He will retire next year.
- The President is to visit Japan next month. = The President will visit Japan next month.
- We are to get a wage rise in June. = We will get a wage rise in June.
Be + to instead of must
The structure be + to is also used to give orders. In this case, it means almost like must.
- You are to complete the work in two days. (= You must complete the work in two days.)
- He is to report for duty within a week.
Had better instead of should or ought to
- You had better consult a good doctor. = You should consult a good doctor.
Had better may also express a threat.
- He had better be careful.
Have to instead of must
- I have to be there at 10 o’clock. (= I must be there at 10 o’clock.)