section_path: Grammar/Syntax/Auxiliary verb constructions
section_name: Auxiliary verb constructions
paragraph_text: Auxiliary verb constructions
  
  English syntax relies on auxiliary verbs for many functions including the expression of tense, aspect, and mood. Auxiliary verbs form main clauses, and the main verbs function as heads of a subordinate clause of the auxiliary verb. For example, in the sentence the dog did not find its bone, the clause find its bone is the complement of the negated verb did not. Subject–auxiliary inversion is used in many constructions, including focus, negation, and interrogative constructions.
  
  The verb do can be used as an auxiliary even in simple declarative sentences, where it usually serves to add emphasis, as in "I did shut the fridge." However, in the negated and inverted clauses referred to above, it is used because the rules of English syntax permit these constructions only when an auxiliary is present. Modern English does not allow the addition of the negating adverb not to an ordinary finite lexical verb, as in *I know not —it can only be added to an auxiliary (or copular) verb, hence if there is no other auxiliary present when negation is required, the auxiliary do is used, to produce a form like I do not (don't) know. The same applies in clauses requiring inversion, including most questions—inversion must involve the subject and an auxiliary verb, so it is not possible to say *Know you him?; grammatical rules require Do you know him?
  
  Negation is done with the adverb not, which precedes the main verb and follows an auxiliary verb. A contracted form of not -n't can be used as an enclitic attaching to auxiliary verbs and to the copula verb to be. Just as with questions, many negative constructions require the negation to occur with do-support, thus in Modern English I don't know him is the correct answer to the question Do you know him?, but not *I know him not, although this construction may be found in older English.
  
  Passive constructions also use auxiliary verbs. A passive construction rephrases an active construction in such a way that the object of the active phrase becomes the subject of the passive phrase, and the subject of the active phrase is either omitted or demoted to a role as an oblique argument introduced in a prepositional phrase. They are formed by using the past participle either with the auxiliary verb to be or to get, although not all varieties of English allow the use of passives with get. For example, putting the sentence she sees him into the passive becomes he is s een (by her), or he gets seen (by her).