Modal verbs are verbs such as can, could, may, might, must, need not, shall/will, should/ought to. They indicate ability, permission, etc. Modal verbs cannot be used in all the tenses in English, so we need to know their alternative forms as well.
Max’s father is a mechanic. He might retire soon, so he thinks Max should work in the garage more often.
Max can already change tyres, but he has to learn a lot more about cars.
Max must do what he is told and must not touch any dangerous equipment.
Modal verbs are generally only used in the present tense in English. We don’t add an s in the third person singular.
He must do what he is told. (not:He musts …)
For negation and questions, we don’t add an auxiliary verb.
Max need not worry about his future. Max must not touch any dangerous equipment. Can Max change a tyre?
Max can change tyres. (not:Max can to change tyres.)
We can often choose between two modal verbs with similar meanings when we ask questions or make requests. One form is more polite than the other.
Can you repair this flat tyre? Could you repair this flat tyre?
Can we come in? May/might we come in?
Shall he pick the car up tomorrow? Should he pick the car up tomorrow?
Will the car be ready tomorrow? Would the car be ready tomorrow?
We use will to make requests/ask somebody to do something. When we want to make a suggestion using the interrogative form in the 1st person (I, we), we use shall.
Max, will you change that tyre?
Change the tyre, will you?
Shall I change that tyre?
If we want to indicate a situation in the past, we have to use the alternative forms instead of the regular modal verbs.
Max’s father took over the garage from his father. He did not have to worry about his future either. Max’s father also had to learn a lot and had to do what he was told. He was not allowed to touch dangerous equipment. He was expected to work in the garage often. However, Max’s father was not as talented as Max and was not able to change tyres until he was 15 years old.
List – Modal Verbs and Alternative Forms
to have to
Max must do what he is told. His father also had to do what he was told.
not to be allowed to
Max must not touch anything dangerous. His father was not allowed to touch anything dangerous.
to be able to/ could*
Max can already change tyres. His father was not able to/couldn’t change tyres.
to be allowed to/ could*
Max can help in the garage at the age of 12. Max’s father was allowed to help at the age of 13.
not to have to
Max need not worry about his future. Max’s father did not have to worry about his future either.
to be supposed to/to be expected to/to be to
Max should work in the garage more often. Max’s father also was supposed to/was expected to/was to work in the garage often.
Of course, we can also use the alternative forms (except for could) in other tenses.
Max can change tyres. = Max is able to change tyres.
* We use could and was/were able for the past of can. We use could for general ability and with the verbs feel, hear, see, smell, taste, remember and understand. We use was/were able to when we talk about something specific in the past. The negative couldn’t can be used in all three cases.
Max’s father could do everything in the garage. Max’s father couldremember changing his first tyre. Was Max able to change the tyre yesterday? Max’s father couldn’t work in the garage alone.