Single-Word Modals and Periphrastic Modals

Single-Word Modals and Periphrastic Modals

We have already seen several single-word modals (modal aux-words). 

can  could  would  should  may  might  must  will  won’t  shall

There are also modals composed of several words. These are called periphrastic modals.    

■ Single-word modal: can (ability)   

   Periphrastic modal:   be able to, am/is/are/was/were able to

   Same meaning:          I can help him. I am able to help him.

■ Single-word modal: may (permission)

   Periphrastic modal:  be allowed to or be permitted to,

                                       am/is/are/was/were allowed to,

                                      am/is/are/was/were permitted to

   Same meaning:          You may not smoke in restaurants in this state.

                                      You are not allowed/are not permitted to smoke in restaurants.

■ Single-word modal: must (need, necessity, obligation, or duty)

   Periphrastic modal:  have to

   Same meaning:          Excuse me, but I must go now.

                                      Excuse me, but I have to go now.

Important:  You cannot have two single-word modals in a row. The second one must change to a periphrastic modal.

Wrong:  I passed my test, so next semester I will can take Level 7.

Right:     I passed my test, so next semester I will be able to take Level 7.

Wrong:   Before you go to Level 5, you must can write yes/no questions.

Right:     Before you go to Level 5, you must be able to write yes/no questions.