The Present Perfect Continuous Tense

The Present Perfect Continuous tense refers to an action that started in the past and it's still in progress at the moment of speaking.

• I have been trying to forget you, but I can't.
  
• He's been searching for an answer for a long time now.
• They've been pen pals since their childhood.
  

Formulation of the Present Perfect Continuous tense

We form this tense by using the auxiliary verb 'to be' in the present perfect tense plus the present participle (the -ing form) of the main verb:

• I have been watching you.
• You have been counting the days.
• He/She/It has been playing all morning.
• We have been studying English for 3 years.
• You have been waiting for Christmas since August!
• They have been talking on the phone for 3 hours by now.
  

Usage of the Present Perfect Continuous tense

The Present Perfect Continuous tense is used for actions that started in the past and are still in progress at the moment of speaking (the moment NOW). So, if I tell you how long the action has been taking place, we are referring to the part of the action that is completed so far, hence the need of the perfect aspect of the verb. However, the action is still continuing, hence the need for the progressive aspect.

They've been playing for 2 hours.  [It is now 4pm.] => They've been playing since 2 o'clock.

We can use two different expressions for specifying the time element.

• We can point to the duration of the activity, by using the preposition 'for'; or
  
• We can use the preposition 'since' to indicate the starting moment.

[He is 10]=> He's been studying English for 3 years./He's been studying English since he was 7.

Confusion between the Present Perfect Continuous and the Present Perfect tense

These two verbs are sometimes interchangeable. The main difference is that the Present Perfect Continuous gives the action in question an added sense of continuity in the present. Consider:

1. My uncle has been working with China Telecom for over 20 years.
2. My uncle has worked with China Telecom for over 20 years.
3. My uncle has been working China Telecom.
4. My uncle has worked with China Telecom.

In examples 1. and 2. there is a sense of the action still continuing in the present and this is more evident in the first sentence than in the second one. However in examples 3. and 4. (where the element of the duration is absent) the actions are clearly different. In example 3. it is evidently continuing in the present, but in example 4. it is obvious that the work with the company stopped before the moment of speaking.