Perfectives are formed by using "have" with the past participle form of verbs. They are commonly used with perfect tenses and unreal conditionals. In addition, perfectives can be used with modals to indicate past possibility and obligation.
Modals + Perfectives
Modals can be combined with perfectives to express past possibility and obligation.
Subject + modal + have + verb in past participle + ...
Note: A modal is always followed by "have" because a modal requires the base form of the verb after it. So, a modal cannot be followed by "has" or "had".
Could/May/Might + Perfective
To indicate a possibility that occurred in the past, you can use these modals with perfectives.
Subject + could/may/might + have + verb in past participle + ...
- Example: It might have rained yesterday, but I am not sure.
- Example: You could have stayed here last night.
- Example: Alex may have reached there by yesterday.
- Example: I saw a mobile phone on my sofa; Neel might have left his phone.
- Example: We could have gone elsewhere; this place is horrible.
Should + Perfective
To indicate an obligation that was supposed to occur in the past but did not happen, you can use "should" with perfectives.
Subject + should + have + verb in past participle + ...
- Example: You should have come yesterday.
- Example: He should not have done this.
- Example: I should have completed the task within the due date.
- Example: They should not have hit him.
- Example: I should have bought that phone.
Must + Perfective
"Must + perfective" is used to express a logical conclusion about a past event. It does not indicate probability or obligation, but rather a firm conclusion.
Subject + must + have + verb in past participle + ...
- Example: It must have rained yesterday.
- Example: He must have eaten something unhygienic.
- Example: Alex must have gone to sleep.
- Example: She must have moved the table.
- Example: She must have studied hard.