17.1 Definition

The English perfect is a verb form used to express completed action. Most such actions are past from the point of view of the speaker: an example is the sentence Jill has done her homework, where the verb form has done indicates that the action of Jill doing her homework is completed. But an action can be described as completed even if it did not happen in the past: for example, in the English sentence Jack can watch television after he has done his homework, the verb form has done describes the action of Jack doing his homework as completed with respect to the action of the main clause, even though it has yet to happen from the speaker's point of view.

The perfect does not necessarily have to refer to a past event because it primarily expresses an aspect rather than a tense (§ 12.9.2). As such, it is different from the past tense, which always describes past action: for example, the sentence Jack did his homework can only refer to a past event, not one that has yet to happen.