verbs may, can, and shall, with most including also be, do, and have. Auxiliary verbs as heads Modern grammars do not differ substantially in the list of auxiliary verbs, though they have refined the concept and often reconceptualized auxiliary verbs as the heads of a verb phrase, rather than as a subordinate element in it. This idea was first put forward by John Ross in 1969. Many pedagogical grammars maintain the traditional idea that auxiliary verbs are subordinate elements, but many modern grammars such as The Cambridge Grammar of the English Language take auxiliaries to be heads. This is shown in the following tree diagram for the clause I can swim. The clause has a subject noun phrase I and a head verb phrase, headed by the auxiliary verb can. The VP also has a complement clause, which has a head VP, with the head verb swim. Auxiliary verbs vs lexical verbs The list of auxiliary verbs in Modern English, along with their inflected forms, is shown in the following table. Some linguists consider membership in this syntactic class the defining property for English auxiliary verbs. The chief difference between this syntactic definition of "auxiliary verb" and the traditional definition given in the section above is that the syntactic definition includes forms of the verb be even when used simply as a copular verb (in sentences like I am hungry and It was a cat) where it does not accompany any other verb. In Modern English, auxiliary verbs are distinguished from lexical verbs by the NICER properties, as shown in the following table. Negation Every case of clausal negation requires an auxiliary verb. Up until Middle English, lexical verbs could also participate in clausal negation, so a clause like Lee eats not apples would have been grammatical, but this is not longer possible in Modern English. Inversion Although English is a subject–verb–object language, there are cases where a verb comes before the subject. This is called subject-auxiliary inversion because only auxiliary verbs participate in such constructions. Again, in Middle English, lexical verbs were no different, but in Modern English *eats Lee apples is ungrammatical. Contraction of not Most English auxiliary verbs – but no lexical verbs – have a negative -n't morpheme. A small number of defective auxiliaries verbs don't take this morpheme. The auxiliary may never takes this morpheme. Am becomes ain't only in non-standard English varieties; otherwise it