Auxiliary Verb Equivalents

Be able to

Be able to can be used to talk about ability. It often has the same meaning as can/could.

• He is able to support her. (He can support her.)
• They were able to catch the thief. (They could catch the thief.)

Be + infinitive

Be + infinitive is used to indicate simple future, like shall or will, but perhaps with a slight degree of uncertainty.

• He is to retire. (It is not certain whether he will actually retire or not.)
• We are to have a test in English next week. (It is not certain whether the test will actually take place.)

Be + infinitive can also have a similar meaning to 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. (He must report for duty within a week.)

Had better

Had better can have the same meaning as should or ought.

• You had better get some rest. (= You should/ought to get some rest.)
• We had better consult a doctor. (= We should/ought to consult a doctor.)

Have to and have got to

• I have to be there by 10 o’clock. (I must be there by 10 o’clock.)
• Did you have to do that? (Was that necessary?)
• I have got to see her.