Auxiliaries are a type of verb, however, they are sufficiently different from main verbs for them to be treated separately in this grammar. They are used to mark tense (the time at which an action takes place) and aspect (the nature of the passage of time during the action). The auxiliary can be dropped from a sentence if it is obvious from context, or is the same as that of the sentence immediately prior. They are a closed class.
Auxiliary stacking gives a poetic or archaic nuance.
The three tenses are past, present and future. In conversation, the tenses tend to mark the time at which the action began or occurred.
On the other hand, narratives are mainly told in present tense. The other tenses are then used relatively, so that past tense is used for things that happened earlier than the narrative present, and the future tense for things that happened later.
The aspects of positive polarity can be categorised in two different ways. Each of these has two possibilities, and thus there are four altogether:
There is a single category of auxiliaries with the opposite polarity — the negative.
Episodic and Generic
The difference between episodic and generic markers is one of extent. Events in episodic sentences take place over a finite duration; generic ones are prototypically unbounded, although this doesn’t literally have to cover all of time.
Activity versus State
The difference between activity and state for most verbs is one of focus, ie.: emphasis can be placed on the event itself (activity), or on the results (state).
Perceptive verbs are treated slightly differently. Here, dynamic and habitual markers act as normal, however, the stative and gnomic are used to denote an ability to perceive a stimulus.
The negative aspect is used for actions, attributes and perceptions which do not occur. These act as the negation of any other aspectual marker. That is, while positive sentences can be classified by aspect, negative sentences all use the same auxiliaries.