Introduction to auxiliary verbs

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Introduction to auxiliary verbs

There are two main categories of verbs: ordinary verbs and auxiliary verbs.

Auxiliary verbs allow us to:
•  conjugate verbs in tenses other than the present and the past simple (eg.: will for the future, would and should for the conditional);
•  express notions of ability, obligation, probability, repetition, among others (eg.: can, must, may, etc.);
•  express the passive voice (e.g.: 'The apple was eaten').

Note the difference between:
•  irregular auxiliary verbs be, have and do, which can also be used as ordinary verbs ('be', 'have' and 'do');
•  modal auxiliary verbs: must, can, could, may, might, will, would, shall, should, ought to, etc.

Some important characteristics:

•  To form the negative, we just need to add not after the auxiliary verb (with these verbs, the construction do not/doesn't/didn't is not used, as in the case for ordinary verbs):
I will not come. [or won't: contracted form]

She cannot read his handwriting. [or can't: contracted form]

You mustn't believe everything he tells you. [or must not: non-contracted form]

Ordinary verb:
I do not want to come. [or don't: contracted form]

•  In the spoken negative form, not is contracted and changes to -n't:
is not=isn't
have not=haven't
must not=mustn't
will not=won't
do not=don't

•  Modal auxiliaries are followed by a verb in the infinitive without 'to' :
I must leave. I have to leave.
He should come. It would be good for him to come.

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