Course paper on theoretical grammar

How to conjugate the perfect continuous tense

One of the more complicated tenses in English, the perfect continuous tense combines the perfect and continuous tenses at the same time. It’s largely used like the perfect tense, but with ongoing or continuous actions.

How to conjugate the present perfect continuous tense

The present perfect continuous tense describes an ongoing action started in the past that continues to the present. If that sounds familiar, it’s because that’s one of the situations we use the normal present perfect tense, too. 
So what’s the difference? The present perfect and the present perfect continuous can often be used interchangeably, but the big difference is emphasis. The present perfect continuous emphasizes that the event is ongoing, whereas the present perfect alone emphasizes completion or achievement. 
To form the present perfect continuous, add the conjugated form of have, the word been, and the present participle. 
has/have + been + [PRESENT PARTICIPLE]
The town has been mining gold since the 1800s. 
I’ve been locked in my closet for hours! 

How to conjugate the past perfect continuous tense

Like the past perfect, the past perfect continuous tense is used in complex and compound sentences to show which event happened first. While the past perfect tense describes an individual action, the past perfect continuous shows an ongoing action that is already finished. 
Form the past perfect continuous tense by adding the words had been before the present participle. 
had been + [PRESENT PARTICIPLE]
Until the moment our picnic began, the sun had been shining all day. 
She had been waiting for a sign before she finally asked him out. 

How to conjugate the future perfect continuous tense

The future perfect continuous tense functions just like the future perfect tense, except with an ongoing action. The major difference is that with the future perfect tense, the event will have ended, but with the future perfect continuous, the event would still be happening by that time in the future. Both, however, are frequently used with expressions of time. 
The future perfect continuous tense is formed by adding the words will have beenbefore the present participle. 
will have been + [PRESENT PARTICIPLE]
In a few weeks, she will have been studying English for a whole year. 
By 6:00, we will have been stuck in this elevator for four hours.