The present perfect continuous tense is a verb tense that shows that something started in the past and is still continuing in the present. It is used to describe an action that is ongoing or incomplete. The present perfect continuous is formed using the present perfect of the auxiliary verb to be and the present participle of the main verb.

“I have been studying for hours.” (The action of studying started in the past and is still continuing up to the present.)

“She has been working on that project for weeks.” (The action of working on the project started in the past and is still continuing up to the present.)

#1. The Present Perfect Continuous is formed by means of the Present Perfect of the auxiliary verb to be and Participle I of the notional verb.

#2. In the interrogative form, the first auxiliary verb is placed before the subject. And in the negative form, the negative particle not is placed after the first auxiliary verb.

#3. The contracted affirmative forms are:

I’ve been working
He’s been working
You’ve been working

The contracted negative forms are:

I haven’t been working
He hasn’t been working
We haven’t been working

#4. The negative-interrogative forms are:

Has he not been working? = Hasn’t he been working?

Have you not been working? = Haven’t you been working?

We distinguish two uses of the Present Perfect Continuous: the Present Perfect Continuous Inclusive and the Present Perfect Continuous Exclusive.

#1. The Present Perfect Continuous Inclusive is used to denote an action which began in the past, has been going on up to the present and is still going on.

The Present Perfect Continuous Inclusive is generally used with since (denoting the starting point of the action), for (denoting the whole period of duration), these two days, etc. (If the conjunction since introduces a clause, the verb in this clause is in the Past Indefinite.)

I have been looking out for your white dress for the last ten minutes. (Bennett)
Ever since I saw you last I have been thinking, thinking. (Dreiser)

As has been stated above the Present Perfect Inclusive is used to denote an action which began in the past, has been going on up to the present and is still going on with verbs not admitting of the Continuous form, in negative sentences and with certain non-terminative verbs.

With verbs not admitting of the Continuous form the Present Perfect Inclusive is the only tense possible.

With verbs in the negative form the Present Perfect Continuous Inclusive can be used, but it is far less common than the Present Perfect Inclusive.

With certain non-terminative verbs both the Present Perfect Inclusive and the Present Perfect Continuous Inclusive are used.

We have worked at the problem for several months. (The fact is emphasized.)
We have been working and working at the problem for months and I don’t think we are likely to solve it. (Locke) (The process is emphasized.)

#2. The Present Perfect Continuous Exclusive denotes an action which was recently in progress but is no longer going on at the present moment.

You are not well to-day. You look distressed. You have been weeping.(Dickens)

The Present Perfect Continuous Exclusive is used to express repeated actions in the past.

How have you been spending your money? I have been buying pictures. (Locke)
I have been getting letters from him.

The Present Perfect Continuous Exclusive is often used with an emotional colouring.

I suppose you have been telling lies again. (Marryat)
Your eyes are red. You have been crying.

Students should take care not to mix up the Present Perfect Continuous and the Present Continuous: the Present Continuous is used to denote an action going on at the present moment, no previous duration is expressed. The Present Perfect Continuous Inclusive is used when the previous duration of the action is expressed.

I am reading Dombey and Son.
I have been reading Dombey and Son for three days.

The Present Perfect denotes a completed action while with the Present Perfect Continuous Exclusive there is an implication of incompleteness.

He has made some experiments. Он сделал несколько опытов. He has been making experiments.
Why are your lips black? I have been eating blackberries. I have eaten a whole plateful.
She is walking up and down the room thinking of the letter she has been writing and wondering how she should finish it.
She is going to post the letter she has just written.