Perfect continuous tenses. Past perfect continuous Present perfect Continuous Future perfect continuous Past perfect continuous

Perfect continuous
tenses.
Past perfect
continuous
Present perfect
Continuous
Future perfect
continuous
Past perfect continuous
We use the past perfect continuous
a) to put emphasis on the duration of an action which stated and finished in the past before another past action or stated time in the past, usually with since or for.
They had been looking for a house for six months before they found one they liked.
b) for an action which lasted for some time in the past and whose result was visible in the past.
He had been waiting at the airport for three hours.
Note : the past perfect continuous is the past equivalent of the present perfect continuous.
Present perfect continuous
We use the present perfect continuous
a)to put emphasis on the duration of an action which started in the past and continues up to the present.
Sam has been talking on the phone for half an hour
b) the action which started in the past and lasted for some time.
The action may have finished or may still be going on.The result of an action is visible in the present.
Her feet hurt.She has been walking all morning.
c) to express anger , irritation or annoyence.
Somebody has been giving away our plans
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Future perfect continuous
We use the future perfect continuous
To emphasis the duration of an action up to certain time in the future
By the end of the next month she will have been teaching for twenty years.
Note: After the time expressions by the time ,until ,before ,we use the present simple because they introduce time clauses.The future perfect and future perfect continuous may come either before or after the time clause.
By the time they reach York , they will have been traveling for four hours.
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