Perfect Tenses
Perfect tenses describe a finished action by referring to the complete (perfect) nature of the action expressed by the verb rather than its timing.
There are three perfect tenses in English:
The main function of a perfect tense is to show that the action expressed by the verb is complete and that there is a clear end to it.
The action may, however, be completed in the present, in the past or in the future.
Linguistic Note
Technically speaking perfect tenses belong to the grammatical category of Aspect. Aspect refers to the nature of the action described by the verb. There are three aspects: indefinite (or simple), complete (or perfect), continuing (or progressive).
In linguistics, the grammatical aspect of a verb defines the temporal flow (or its lack) in the described event or state. For example, in English the difference between I walk and I am walking is a difference of aspect, not tense.
Tense and aspect are formally separated in the English language but when it comes to everyday usage the two tend to merge and we generally talk about perfect tense rather than perfect aspect.
