In other words, English distinguishes among four distinct aspects, tense aside:
The tense of the verb "to have" dictates the time of the consequences but not of the action. For example, in the above sentence "I have written a novel," the novel is clearly finished at present: the present tense of the verb "to have" indicates that the consequences -- the state of being an author with a completed novel -- are being considered in the present tense, even though the authorship is in the past tense.
In addition, the past progressive tense ("I was writing a novel") may connote that an action was interrupted: this connotation can also carry over into the pluperfect progressive tense ("I had been writing a novel").
The passive voice can normally be combined with the perfect aspect, but English speakers tend to frown on passive perfect progressives when they form the construction "been being," as in "the novel has been being written for ages now," the passive form of "I have been writing the novel for ages now."
Outside of the indicative mood, the perfect aspect has only a limited proper existence. Because the English modal verbs are largely defective, and because the English subjunctive mood by itself does not form a true preterite, the verb "to have" is often used to construct past tenses. For example, while "I could write a novel" is allowed by English, "I could wrote a novel" is ungrammatical, and instead the form "I could have written a novel" is used. These tenses are often called perfect by analogy, but the perfect aspect only exists properly when it can be contrasted with an imperfect aspect, since it is defined by a subtle difference in where the listener places their attention.
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