Verbs in Proto-Søkkli are basically perfective or imperfective. Perfective verbs can be turned into imperfective ones by either an imperfective ending or a subsequent attached verb which is marked as imperfective. Imperfective verbs can be turned into perfective ones by prefixing the verb with a perfective coverb; attaching subsequent verbs that are perfective has no effect, even though typically if there is a choice an attached verb will be marked as imperfective.
Subverbs are like verbs in this regard, except that they can also be neutral, where they do not affect the perfectivity of the verbs to which they are attached.
Perfectivity means that an event is singular in nature and has no internal structure. This is often used to mark events that are momentary or the starts or ends of events.
Imperfectivity means that an event has internal structure. This is often used to mark events that took place over a period of time, habitual events, repeated events, corresponding to progressive, habitual, and iterative aspects in other languages.
In discourse background information is commonly in imperfective aspect while foreground information is commonly in perfective aspect.