Auxiliary verb
English verbs are limited as to what they can indicate on their own, i.e. through their own morphology. Morphological inflexions can be used, for example, to show that an event occurred in the past (e.g. cooked) and in the present (e.g. cook); they can also show third person agreement (e.g. she cooks) and continuous action (e.g. cooking).
More often, the main verb needs to be linked with a secondary verb form which accompanies it to create a verb phrase. These secondary verbs are called auxiliaries. Auxiliary verbs are used, for example, to give a sense of time to the main verb (e.g. ‘He will be working soon.’) or to create a question, ‘Have you won?’, ‘Do you believe it?’, ‘Could it be true?’
Common auxiliary verbs are forms of to be (is/am/was/are/were/will), to have (has/had/have) and to do (does/did).
Some auxiliary verbs are used to indicate that an action is only potential. These are called modal auxiliaries, e.g. may, might, would, could, should.
