Primary auxiliary verb

From Teflpedia

A primary auxiliary verb is a primary verb used as an auxiliary verb.

There are three of these in English:

Auxiliary verb Parent verb Notes
Auxiliary do do The default, used in the absence of aspect or modality.
Auxiliary have have Used to mark the perfect aspect.
Auxiliary be be Used with the continuous aspect, and also as standalone be.

Auxiliary have and auxiliary be can be used together or with a full modal verb, e.g. They could be having fun.

Contrast full modal verb.