Past future perfect tense is a verb form to discuss activities that would have been done in the past. This form is commonly used in the main clause of a conditional sentence type 3
Past future perfect tense is formed with the auxiliary verb and would or should have, and the past participle (verb-3) . Have used both for singular and plural subjects. While past participle can be either regular or irregular verb.
Types of sentences
Formula
Example
Positive
( + )
S + would/should + have + V-3/past participle
I/you/she/he/it would have worked
They/we would have been
Negative
( - )
S + would/should + not + have + V-3/past participle
I/you/she/he/it wouldn’t have worked
They/we wouldn’t have been
Interrogative
( ? )
Would/should + S + have + V-3/past participle
Would I/you/she/he/it have worked
Would they/we have been
Function
Example in sentence
Past future perfect tense to indicate that an action is expected to have completed at some time in the past. In this case, would have a version of the "past" of the future perfect tense will have.
I thought you would have slept by the time I arrived.
Before taking a leave of absence yesterday, he would complete his work for the client. He would have submitted it two days ago.
Past future perfect tense used in the conditional sentence type 3 to talk about something that does not happen.
If you had saved your jewelry and foreign currency in a safety deposit box, they wouldn’t have gone.
What/where/when/why/who/how + should/would + subject + have + verb III + Object