AUXILIARY VERB

Also called a helping verb, it is a verb used with a main verb to form a verb phrase. Auxiliary verbs are commonly divided into two groups. The first group includes the forms of do (do, does, did); the forms of has (has, have, had); and the forms of be (am, is, are, was, were, be, been, being) that indicates tense and voice.

Now that we have matured from petty quarrels and silly competitions, we have learned that there is no need of being rivals.

The second group includes modals, such as can, which indicates a current ability; could, which indicates an ability sometime in the past; may, which indicates a weak possibility or asks for and gives permission; might, which indicates a stronger possibility than may; must, which indicates obligation or necessity, or, in the present tense, a certainty; should, which indicates an advice or an obligation of a somewhat lesser degree than must, or a degree of certainty of a somewhat lesser degree than must; ought to, which indicates an obligation of a degree somewhat more than should and somewhat lesser than must; shall, which indicates an option, intention, or suggestion to do something; will, which indicates willingness to do something in the present; would, which indicates an invitation to do something or a past or a present willingness to do something.

I can not believe that my twin sister would stay at home rather than breathe the fresh air out here.