3.3 Present perfect

Form: present perfect

have / has + past participle

The present perfect is formed with have / has (the present tense forms of have) + the past participle form of the verb.

Affirmative

The following contracted forms are often used in spoken and in informal written language:

I have » I've
you have » you've
he/she/it has » he's/she's/it's
we have » we've
you have » you've
they have » they've

Negative

The contracted forms haven't and hasn't are often used instead of have not and has not in spoken and in informal written language.

Interrogative

Present perfect for past events

The present perfect tense is used for past events when the exact time is not mentioned either because it is not known or it is not important. The emphasis is on the fact that the events happened before the time of speaking:

I've been to China.
I've seen that film before.

But if we say when something happened, we use the past simple:

I went to China in 2011.
I already saw that film last week.

We also use the past simple if we ask when something happened in the past:

"Have you ever been to China?"
"Yes, I have."
"When did you go there?"

"Have you seen that film before?"
"Yes, I have."
"When did you see it?"

Present perfect for recent events with a result in the present

The present perfect tense is used for recent events that have a result in or an effect on the present moment:

Someone has opened the window. (the window is open, and it is cold inside)
Tom has broken his leg. (his leg is broken, and he can't walk)

If there is no connection between the action and the present moment, the past simple is used:

Someone opened the window to let in some fresh air. (the window is now closed, or we don't know whether it is closed or not)
On the day before the match, Tom broke his leg. (his leg is not broken anymore)

Present perfect with an incomplete period

The present perfect tense is used to express actions happening in an incomplete period of time. An incomplete period is one that includes the present moment, that is, the time of speaking. This period can be implied or expressed with a time expression (today, this week, this year, ever, never etc.):

I haven't smoked today.
I've lived here all my life.
Have you ever been to China? (in your life)
My uncle has written several plays. (in his life, supposing he is still alive)
He has never worked as a waiter. (in his life)

If the action happened in a completed period of time (one that does not include the time of speaking), the past simple tense is used. This period can be implied or expressed with a time expression (yesterday, last week, last year, between 1905 and 1910 etc.) or a clause:

I didn't smoke yesterday.
I lived in this house when I was a child. (I am not a child any more)
Did you go to China when you were working as a flight attendant?
Shakespeare wrote numerous plays. (in his life, he is dead now)
He worked in this café between 1905 and 1910.

Note that some time expressions (e.g. this morning, recently and lately) may refer to either a completed or an incomplete period of time depending on the context and whether or not the time of speaking is included in the given period:

I have seen him this morning. (it is still morning)
I saw him this morning. (it is later during the day)

He has put on some weight recently. (in the past few days/weeks/months etc.)
He put on some weight recently. (some time ago)

Reference to an incomplete period of time, however, does not always involve the use of the present perfect tense:

Have you been to Lake Balaton this year? (any time this year)
Did you go to Lake Balaton this year? (at the time when you go there every year)

Although both actions are related to an incomplete period, the present perfect in the first sentence refers to an indefinite time; meanwhile, the past simple in the second sentence implies a definite time (supposing the recipient of the question always visits Lake Balaton at the same time every year).

Present perfect with FOR and SINCE

The question words how long? and since when?, and the prepositions for and since are used with the present perfect tense to express that something started in the past and is still true. How long? and for refer to an incomplete period of time, while since when? and since refer to a point in time:

I have lived here for two months.
I have lived here since January.
"How long have you known José?" "For ten years."
"Since when have you known José?" "Since the early 1990s."

The point in time after since can also be expressed with a clause containing a verb in the past simple:

I have lived here since I was born.
I've known José since we were young.

Present perfect with JUST

The present perfect tense is used for recently completed actions, usually with the word just:

I have just started a typing course.

If the exact time is mentioned, the past simple is used:

I started a typing course a few weeks ago.

Just now also requires the past simple tense and means "a moment ago":

I spoke to him just now. He says hi.

Present perfect with YET and ALREADY

The time expressions yet and already are often used with the present perfect tense. Yet is used in negative and interrogative sentences:

I haven't finished yet.
Have you talked to him yet? 

Already is usually used in affirmative sentences:

I've already told you more than I should.

IT'S (BEEN) + DAYS / WEEKS / MONTHS / etc. + SINCE

The structure it's (been) + days / weeks / months / etc. + since is used to emphasise the length of time that has passed since a past event:

It's been weeks since his last blog post.
It's been a long time since I met him.
How long has it been since they moved away?

In the sentences above, it's been stands for it has been (present perfect); however, in everyday speech, it is more common to use the present simple instead of the present perfect:

It's weeks since his last blog post.
It's a long time since I met him.
How long is it since they moved away?

Present perfect with quantities

The present perfect tense is used to express quantities: how much we have done of something or how often we have done something in an incomplete period of time:

I've written two letters today.
How much alcohol have you consumed in the past 24 hours?
I've been to the cinema three times this month.

Present perfect with superlative forms of adjectives

The present perfect is used with superlative forms of adjectives to express emphasis:

This is the first time I have been to the Philippines.
This is the worst film I have ever seen.