Past and Present of Modals

2. Relationships among the modal auxiliaries

Just as would can be used as the past of will; could can be used as the past of can; might can be used as the past of may; and should can be used as the past of shall. The auxiliary must can refer either to the present or to the past. These relationships among the modal auxiliaries can be summarized as follows:

Present	Past
can	could
may	might
must	must
shall	should
will	would

The following examples illustrate these relationships:

Tense of Verb in Main Clause	Complete Sentence
Simple Present	I think I can do it.
Simple Past	I thought I could do it.
Simple Present	He predicts it may rain.
Simple Past	He predicted it might rain.
Simple Present	She knows she must be there.
Simple Past	She knew she must be there.
Simple Present	I wonder what we shall do tomorrow.
Simple Past	I wondered what we should do the next day.

See Exercises 4 and 5.

Each of the modal auxiliaries has more than one meaning. The meaning depends upon the context in which the auxiliary is used. 



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ENGLISH GRAMMAR:  EXPLANATIONS AND EXERCISES  by Mary Ansell