Auxiliary verbs

Here is a list of auxiliary verbs (see also modal verbs):

Auxiliary verb	All forms	Short affirmative forms	Short negative forms
• DO	do, does did		don't, doesn't, didn't
• BE	be am, is, are was, were.	am = 'm is = 's are = 're	'm not, isn't, aren't wasn't, weren't.
• HAVE (=haber)	have, has had	have = 've has = 's had = 'd	haven't, hasn't hadn't
• WILL		'll	won't
• WOULD		'd	wouldn't
• CAN	can could		can't, couldn't. Special written form: cannot (yes, one word only).
• MUST	must, have to had to		mustn't Remember to write the final T in MUST, then add N'T.
• SHALL		'll	shan't
• SHOULD			shouldn't
• OUGHT TO			oughtn't
• MAY			mayn't (It is very rarely used.)
• MIGHT			mightn't

Some verbs are "semiauxiliary" (they do not always follow the rules for auxiliary verbs).
A special case is "HAVE", which has different meanings and can be used in different ways:

Auxiliary verb	All forms	Short affirmative forms	Short negative forms
• HAVE GOT	have, has	have got = 've got has got = 's got	haven't (got), hasn't (got)
• HAVE (GOT) TO	have (got) to, has (got) to had to	have (got) to = 've got to has (got) to = 's got to	don't have to, doesn't have to didn't have to
• NEED	need, needs		needn't
• DARE	dare, dares		daren't

An auxiliary verb has three characteristics:
A main verb functions in a different way (it has different characteristics):
Some verbs can function as main verbs or auxiliaries (see more details below).
All other verbs are either auxiliaries or main verbs.

Notes:

BE is an auxiliary verb. It can also be the main verb of a sentence, but it still works as (i.e. has the characteristics of) an auxiliary verb:
HAVE GOT can be used as an auxiliary verb (haven't got) in the present only, but in the past it is always used as a main verb (didn't have).

HAVE (GOT) TO can be used as a main verb (don't have to) or as an auxiliary (haven't got to) in the present, but always as a main verb in the past (didn't have to).

NEED can be used as a main verb in the present (doesn't need to) and in the past (didn't need to), but it can also be used as an auxiliary (needn't) in the present only, and of course if it is followed by a main verb:

I don't need to wash my hands. = I needn't wash my hands.
I don't need any soap.

DARE, like NEED, can also be used as a main verb in the present (doesn't dare to) and in the past (didn't dare to), but as an auxiliary (daren't) in the present only.

USED TO is an auxiliary verb (it is always followed by another verb in the infinitive), but it is used as a main verb (didn't use to). In Spanish it is translated as the "imperfect past" (jugaba) or as "soler" (solía jugar).

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