Perfect Form

On this page:
Why do we use a perfect?
How do we make a perfect?
Examples of perfects: past, present, and future.

Why do we use a perfect form?
Many English sentences say that something happens at a time.
1A. She went when I arrived.
This sentence says that the two actions, went and arrived, happen at one time.
She went
↕
I arrived

If we want went to be before arrived, we use a perfect form.


How do we make a perfect form?
Example 1A. She went when I arrived.
To make a perfect form of the same sentence, we can change the verb went.

A perfect form uses some form of have and then a past participle (the —en/ed/t form of a verb). As usual, we put the tense on the first part of the verb: because went is the past tense of go, we need the past tense of have, which is had.
She had

Then, we add the —en/ed/t form of the verb go, which is gone.
She had gone

When we put this into the sentence, the times are different. A perfect form tells us that there are 2 times, one which is before the other.
1B: She had gone when I arrived.

Now, I did not see her, because had gone is before arrived.
had gone←←←←↓arrived

If we make arrived perfect, the times change again, because then had arrived is before went.
She went when I had arrived.
had arrived←←←←↓went

Example 2A: He takes many photos.
This sentence is talking about a habit, something which I usually do, because the verb takes is present simple tense.
He takes
↓↓↓↓↓↓↓↓
If we want to talk about time before now, we can use a perfect form.

As usual, we put the tense on the first part of the verb: because takes is present tense, we need the present tense of have, which is has.
He has

Then, we add the —en/ed/t form of the verb take, which is taken.
He has taken

When we put this into the sentence, the times are different.
2B: He has taken many photos.
has taken ←←←←←←↓now
This does not say an exact time before now: it can mean my whole life, or only today, or any other time before now.

Example 3A: I will finish this book on Friday. You can borrow it on Saturday.
The first sentence says something will happen at a time. If we want to change the sentence to say before a time, we can use a perfect form.

As usual, we put the tense on the first part of the verb. Because will finish is the future tense of finish, we need the future tense of have, which is will have.
I will have

Then, we add the —en/ed/t form of the verb finish, which is finished.
I will have finished

When we put this into the sentence, the times are different.
3B: I will have finished this book on Friday.
This means I will finish the book before Friday. You can borrow it on Friday.

More examples
I woke up and saw that someone had stolen my car.
When she became a doctor, she had spent six years at university.

Someone has stolen my car!
You have passed your exam. Well done!

Hopefully, the police will have found my car by the time work starts on Monday.
Next year, we will get 200 more students, but we will have built 10 new classrooms for them.

We can also use perfects with continuous forms, to make perfect continuous verbs, with passive forms, to make perfect passive verbs, and with infinitives, to make perfect infinitives, which are useful with modal verbs.