Grammar Club

Must (subjective obligation)

Posted on January 15th, 2009 by Admin

Structure of Must

Must is a modal auxiliary verb. It is followed by a main verb. The structure is:

subject + must + main verb

The main verb is the base verb (infinitive without “to”).

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Have to (objective obligation)

Posted on January 12th, 2009 by Admin

Structure of Have to

Have to is often grouped with modal auxiliary verbs for convenience, but in fact it is not a modal verb. It is not even an auxiliary verb. In the have to structure, “have” is a main verb. The structure is:

subject + auxiliary verb + have + infinitive (with to)

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Be able to

Posted on January 10th, 2009 by Admin

Although we look at be able to here, it is not a modal verb. It is simply the verb be plus an adjective (able) followed by the infinitive. We look at be able to here because we sometimes use it instead of can and could.

We use be able to:

to talk about ability

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Could

Posted on January 8th, 2009 by Admin

Could is an auxiliary verb, a modal auxiliary verb. We use could to:

talk about past possibility or ability

make requests

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