Learning to Use the Future Perfect Continuous Tense
The Core Characteristic of the Future Perfect Continuous is to focus on the time period of an imagined past of a future event. Just like for Future Perfect Simple, the Reference Point (R) of Future Perfect Continuous is arrived at by firstly going to the specific future time period that is being described. From there you look backwards at the time period leading up to this event. This time period is connected to the future time period.
|By the time you get here, I will have been working for four hours|
It is interesting to note that the time period of Future Perfect Continuous is not connected to Present time. By this, we mean that if you said By the time you get here, I will have been working for four hours, we cannot tell how far into the future that will be. It could be 4 hours from now, but it could be less, or it could be more. I could have started working 1 hour ago, in which case, you will get here in three hours. Equally, you might not leave for another 6 hours, which means that I will only start working in 2 hours time.
As the time period of the Future Perfect Continuous is not linked to Present time, it is not known when the action began (Past, Present or Future). This information can only be worked out by working back from the nominated future time.
In Diagram 1, both actions are in the future, but remember, this statement doesn't tell us when the action began. Therefore it is also possible that the person who made the statement could have already started working. They could have already done one hour of work (see Diagram 2, next page).