List of auxiliaries in English Diagnostics for identifying auxiliary verbs in English

Diagnostics for identifying auxiliary verbs in English

The verbs listed in the previous section can be classified as auxiliaries based upon two diagnostics: they allow subject–auxiliary inversion (the type of inversion used to form questions etc.) and (equivalently) they can take not as a postdependent (a dependent that follows its head). The following examples illustrate the extent to which subject–auxiliary inversion can occur with an auxiliary verb but not with a full verb:^[16]
a. He was working today.
b. Was he working today? - Auxiliary verb was allows subject–auxiliary inversion.
a. He worked today.
b. *Worked he today? - Full verb worked does not allow subject–auxiliary inversion.
a. She can see it.
b. Can she see it? - Auxiliary verb can allows subject–auxiliary inversion.
a. She sees it.
b. *Sees she it? - Full verb sees does not allow subject–auxiliary inversion.
(The asterisk * is the means commonly used in linguistics to indicate that the example is grammatically unacceptable or that a particular construction has never been attested in use.) The following examples illustrate that the negation not can appear as a postdependent of a finite auxiliary verb, but not as a postdependent of a finite full verb:^[17]
a. Sam would try that.
b. Sam would not try that. - The negation not appears as a postdependent of the finite auxiliary would.
a. Sam tried that.
b. *Sam tried not that. - The negation not cannot appear as a postdependent of the finite full verb tried.
a. Tom could help.
b. Tom could not help. - The negation not appears as a postdependent of the finite auxiliary could.
a. Tom helped.
b. *Tom helped not. - The negation not cannot appear as a postdependent of the finite full verb helped.
A third diagnostic that can be used for identifying auxiliary verbs is verb phrase ellipsis. See the article on verb phrase ellipsis for examples.
These criteria lead to the copula be and non-copular use of be as an existential verb being considered an auxiliary (it undergoes inversion and takes postdependent not, e.g., Is she the boss?, She is not the boss, Is there a God?, There is a God). However, if one defines auxiliary verb as a verb that somehow "helps" another verb, then the copula be is not an auxiliary, because it appears without another verb. The literature on auxiliary verbs is somewhat inconsistent in this area.^[18]
There are also some properties that some but not all auxiliary verbs have. Their presence can be used to conclude that the verb is an auxiliary, but their absence does not guarantee the converse. One such property is to have the same form in the present tense, also for the first and the third person singular. This in particular is typical for modal auxiliary verbs, such as will and must. (Examples: He will come tomorrow, she must do it at once, not he wills or she musts.)