From Hull AWE
The three verbs 'to be', 'to have' and 'to do' are labelled the primary verbs in Quirk, 1985. They are "the most important verbs in the language" (p. 64). It is a closed sub-class. Its members may be singled out for
- functioning both as auxiliary verbs and lexical verbs;
- having very varied ('irregular') inflections, including the changes in pronunciation of do ('doo', IPA: /duː/) and does ('duzz', IPA: /dʌz/), etc (see Do - does - doesn't - don't (phonetic); and
- having contracted forms, including in negative uses like -'s and -n't in irregular patterns, unlike those of most verbs.