The "going-to" idiom, used to express futurity is a semi-modal verb that consists of a form of the copula verb "be", the word "going" followed by the word "to", for instance "is going to". Like other modals, it is followed by the base infinitive of the main verb (compare with "ought to".) (An alternative description is that it uses the verb "go" in the progressive aspect, most commonly in present progressive form, serving as an auxiliary verb and having the "to"-infinitive phrase as its complement. However this description fails to take into account sentences in which the main verb is elided, such as "Yes, he's going to.") It can be put into question and negative forms according to the normal rules of English grammar.