Perfective and imperfective PROCESSES
According to Langacker, the basic aspectual distinction is between perfective and imperfective, and the semantic basis of this aspectual distinction can be described in terms of scanning. As we have seen, Langacker (2002: 86) defines a PROCESS as ‘a series of profiled relations . . . distributed through conceived time and scanned sequentially.’ This definition as it stands makes no reference to aspectual distinctions, so it applies equally to both perfective and imperfective PROCESSES. However, an imperfective PROCESS is characterised by the fact that each relation that makes up the cognitive representation is the same as the next, which means that the situation described remains constant through time. In contrast, a perfective PROCESS is characterised by a sequence of relations where each is different from the last, which means that the situation described involves change through time.
Langacker (2002: 86) describes verbs like jump, kick and arrive as ‘canonical’ or prototypical perfectives, and verbs like resemble, have and know as prototypical imperfectives. Langacker relies on well-established grammatical tests for distinguishing between the two. Prototypical imperfectives like resemble can occur in the simple present (24a) but not in the progressive (24b).
In contrast, while prototypical perfectives like build can occur in the progressive (25a), they are unnatural in the simple present (25b), unless this gives rise to the habitual or ‘narrative’ senses of the simple present.
However, there are not always clear-cut distinctions between perfective and imperfective categories. As we mentioned above, context can alter the construal of aspect. For example, while perfectives are often odd in the simple present, an appropriate context can license this usage and give rise to a habitual interpretation, which construes the situation as imperfective. Compare the following conversational exchanges:
In example (27), the context of Lily’s utterance, together with her use of the expression every morning, gives rise to a habitual interpretation. Despite this broad division between perfective and imperfective PROCESSES, some verbs can occur quite naturally in both the simple present and the progressive, illustrating that they can be interpreted as either imperfective or perfective, respectively. This is illustrated by example (28).
Example (28a) describes a situation that remains constant over time: Lily has loved the book (or the film) for some time, and this is not expected to end. In contrast, (28b) describes an ongoing experience: Lily is enjoying reading the book or watching the film at the moment, and at some point this activity will come to an end.
