Use modal auxiliaries correctly

In English, we use the modal auxiliary verbs to express a variety of ideas. They are especially common in conditional sentences. Using modal auxiliaries we can express ideas such as probability, ability, possibility, necessity, obligation, willingness, threat, uncertainty etc.

Modal auxiliary verbs are not verbs on their own. They are used with the base form of the verb.

• You must go now.
• She will come.
• It might rain in the evening.

The base form of the verb is the infinitive form minus to. Examples are: take, break, come, watch, sing, play, act etc.

The infinitive can be used with and without to.

The infinitive has simple, simple continuous, perfect and perfect continuous forms.

Study the examples given below.

Simple form: write, take, work

Simple continuous: be writing, be taking, be working

Perfect: have written, have taken, have worked

Perfect continuous: have been writing, have been taking, have been working

These forms can be used after a modal auxiliary verb to express various ideas.

Study the examples given below.

• I may take a break now or later. (This sentence refers to the present or the future.)
• He doesn’t pick up the phone. He may be sleeping. (This sentence refers to the present.
• I might have made a mistake. (This sentence refers to the past.)
• She didn’t pick up the phone when I called. She might have been taking a nap. (This sentence refers to the past.)

As you can see, the simple and simple continuous forms are used to refer to the present or future. The perfect and perfect continuous tense forms are used to refer to the past. Except ‘can’, all other modal auxiliary verbs can be used with the simple and perfect forms of the infinitive. The modal auxiliary ‘can’ can only be used with the simple and simple continuous form of the infinitive.

When the modal auxiliary verbs would, could, must, ought to and should are used with perfect infinitives, they refer to past actions that were not started or completed.

• He should have asked my permission before reading my letters. (He didn’t ask my permission.)
• Did you see him fall? He could have killed himself. (He didn’t kill himself, but that could have happened.)
• He ought to have taken rest after the surgery. (He didn’t take rest.)
• You should have posted the letter yesterday. (You didn’t post the letter yesterday, but it was necessary.)