I could perdure you could perdure he could perdure we could perdure you could perdure they could perdure
V-ing form
I could be perduring you could be perduring he could be perduring we could be perduring you could be perduring they could be perduring
Perfect
I could have perdured you could have perdured he could have perdured we could have perdured you could have perdured they could have perdured
V-ing perfect
I could have been perduring you could have been perduring he could have been perduring we could have been perduring you could have been perduring they could have been perduring
Negation
Simple form
I could not perdure you could not perdure he could not perdure we could not perdure you could not perdure they could not perdure
V-ing form
I could not be perduring you could not be perduring he could not be perduring we could not be perduring you could not be perduring they could not be perduring
Perfect
I could not have perdured you could not have perdured he could not have perdured we could not have perdured you could not have perdured they could not have perdured
V-ing perfect
I could not have been perduring you could not have been perduring he could not have been perduring we could not have been perduring you could not have been perduring they could not have been perduring
Interrogative form
Simple form
could I perdure? could you perdure? could he perdure? could we perdure? could you perdure? could they perdure?
V-ing form
could I be perduring? could you be perduring? could he be perduring? could we be perduring? could you be perduring? could they be perduring?
Perfect
could I have perdured? could you have perdured? could he have perdured? could we have perdured? could you have perdured? could they have perdured?
V-ing perfect
could I have been perduring? could you have been perduring? could he have been perduring? could we have been perduring? could you have been perduring? could they have been perduring?
Interro-negative form
Simple form
could I not perdure? could you not perdure? could he not perdure? could we not perdure? could you not perdure? could they not perdure?
V-ing form
could I not be perduring? could you not be perduring? could he not be perduring? could we not be perduring? could you not be perduring? could they not be perduring?
Perfect
could I not have perdured? could you not have perdured? could he not have perdured? could we not have perdured? could you not have perdured? could they not have perdured?
V-ing perfect
could I not have been perduring? could you not have been perduring? could he not have been perduring? could we not have been perduring? could you not have been perduring? could they not have been perduring?