<Li> They are defective: they are not used as infinitives or participles (except occasionally in non-standard English; see § Double modals below), nor as imperatives, nor (in the standard way) as subjunctives . </Li> <Li> They function as auxiliary verbs: they modify the meaning of another verb, which they govern . This verb generally appears as a bare infinitive, although in some definitions a modal verb can also govern the to - infinitive (as in the case of ought). </Li> <Li> They have the syntactic properties associated with auxiliary verbs in English, principally that they can undergo subject--auxiliary inversion (in questions, for example) and can be negated by the appending of not after the verb . </Li> <Ol> <Li> Jump up ^ However, they used to be declined by person and number, but with the preterite endings . Thus, they often have deviating second person singular forms, which still may be heard in quotes from the Bible (as in thou shalt not steal) or in poetry . </Li> </Ol>

Who uses it but has no need for it