We use the Present Perfect Progressive when we wish to emphasize that an activity has been in progress throughout a period, often with consequences now. Depending on context, this activity may or may not still be in progress at the present time. This use often occurs with all + time references: e.g. all day:

• She is very tired. She's been typing letters all day. (Depending on context, she is still typing or has recently stopped.)

The Past Perfect Progressive, in the same way, is used for activities in progress during an earlier past, often with consequences then:

• She was very tired. She had been typing letters all day. (Depending on context, she was still typing or had recently stopped.)

Some verbs like learn, lie, live, rain, sit, sleep, stand, study, wait, work naturally suggest continuity and often occur with Perfect Progressives with since or for and also in questions beginning with How long ... ?:

• I've been working for Exxon for 15 years. (Depending on context, I am still now, or I may have recently changed jobs or retired.)

• When I first met Ann, she had been working for Exxon for 15 years. (Depending on context, Ann was still working for Exxon then or she had recently changed jobs or retired.)

With 'continuity verbs', simple and progressive forms are often interchangeable, so in the above examples 'I've worked' and 'she had worked' could be used. The only difference is that the Progressive puts more emphasis on continuity.

The Perfect Progressive forms are often used to show that an action is (or was) frequently repeated:

• Jim has been phoning Jenny every night for the past week.

• Jenny was annoyed. Jim had been phoning her every night for a whole week.

We use the Progressive (seldom the Simple) forms to show that we have come to a conclusion based on direct or indirect evidence:

• Your eyes are red. You've been crying.

• Her eyes were red. It was obvious she had been crying.

The Present Perfect Progressive often occurs in complaints:

• This room stinks. Someone's been smoking in here.

The difference between an activity still in progress and one that has definitely been completed is marked by context and by the verbs we use. The simple and progressive forms are not interchangeable here:

Example 1

In the first example, the activity is uncompleted. In the second example, the job is definitely finished.

Example 2

In the first example, the activity was uncompleted then. In the second example, the job was definitely finished then.