Halliday & Matthiessen (1999: 307):
Given that a process takes place in time, there will be some sense in which it has a beginning, a middle and an end. These may be observable as distinct constituents, if it is a process having duration; even if it is instantaneous, however, they represent possible facets, points of view from which it can be considered. In English, the meaning of a process typically includes it completion: if I ‘cut’ a piece of string, I cut it in two. To construe a process as non-completed, English uses conative or inceptive phase: ‘try to cut it’, ‘start to cut it’.