Verb aspect
Introduction
The grammar term aspect is used to indicate the speaker's view of the nature of an action or state. So, the progressive (or continuous) aspect conveys that speaker views the action or state as continuing over a period of time. The perfect (or perfective) aspect conveys that speaker views the action or state as having a completion.
The best way to understand the rather nebulous definitions above is to look at some examples of each aspect.
Progressive aspect
The progressive Some grammarians call this the imperfect aspect. aspect is formed with the verb to be and the present participle of the main verb. It is used in reference to ongoing actions or states in the past, present or future.
- I was walking in the forest at this time yesterday (past).
- I am reading War and Peace at the moment (present).
- I hope I will be living in my own home by the time I'm thirty. (future).
The progressive aspect can combine other forms of to be with the main verb. For example:
- I had been walking in the forest for only 10 minutes when it started to rain (past in the past).
Perfect aspect
The perfect Some grammarians call this the perfective aspect. aspect is formed with the verb to have and the past participle of the main verb. It is used in reference to actions or states in the past or future that have or will have been completed.
- I have made a cake (past).
- By the time I am thirty I will have visited all the countries in Europe (future).
Like the progressive aspect, the perfect aspect can combine other forms of to have with the main verb. For example:
- I had made dinner, but my wife was too tired to eat it when she came home from work (past perfect).
A note about tenses
It is common in the grammar books written for English language learners to refer to the various combinations exemplified above (and many more) as tenses. For example: the present progressive tense, the past perfect tense, the future perfect continuous tense.
Modern grammarians, however, prefer to say that there are only two tenses: present and past. And that all the 'tenses' made with combinations of the auxiliary verbs to be and to have are better called verb constructions.
Conclusion
Questions about when to use a verb with or without an aspect auxiliary in a particular context are common on English language grammar forums.
My general advice to learners on this issue is to bear in mind what Lewis in The English Verb (p85) says:
Aspects give the speaker's temporal interpretation of the event. They do not refer to real time, but to psychological time - to the speaker's perception of the temporal quality of the event.