Auxiliaries like these typically appear with a full verb that carries the main semantic content of the clause.
Auxiliary verbs typically help express grammatical tense, aspect, mood, and voice.
The auxiliary verbs of a language form a closed class, i.e., there is a fixed, relatively small number of them.
[8] Widely acknowledged verbs that can serve as auxiliaries in English and many related[clarification needed] languages are the equivalents of be to express passive voice, and have (and sometimes be) to express perfect aspect or past time reference.
In the case of English, verbs are often identified as auxiliaries based on their grammatical behavior, as described below.
In some cases, verbs that function similarly to auxiliaries, but are not considered full members of that class (perhaps because they carry some independent lexical information), are called semi-auxiliaries.
They list auxiliary verbs, then present the diagnostics that motivate this special class (subject-auxiliary inversion and negation with not).
The modal verbs are included in this class, due to their behavior with respect to these diagnostics.
The following table summarizes the auxiliary verbs in standard English and the meaning contribution to the clauses in which they appear.
African American Vernacular English makes a variety of finer tense/aspect distinctions than other dialects of English by making use of unique variant forms of, in particular: habitual 'be', reduced 'done' (dən), and stressed 'been' (BIN):[14][15] 'She is always telling people she's eight' 'I have (already) pushed it' 'I've known that for a long time' 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.)
[16] (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).
[19][20] The two are similar insofar as both verb types contribute mainly just functional information to the clauses in which they appear.