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 couldn't perdure you couldn't perdure he couldn't perdure we couldn't perdure you couldn't perdure they couldn't perdure
V-ing form
I couldn't be perduring you couldn't be perduring he couldn't be perduring we couldn't be perduring you couldn't be perduring they couldn't be perduring
Perfect
I couldn't have perdured you couldn't have perdured he couldn't have perdured we couldn't have perdured you couldn't have perdured they couldn't have perdured
V-ing perfect
I couldn't have been perduring you couldn't have been perduring he couldn't have been perduring we couldn't have been perduring you couldn't have been perduring they couldn't 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
couldn't I perdure? couldn't you perdure? couldn't he perdure? couldn't we perdure? couldn't you perdure? couldn't they perdure?
V-ing form
couldn't I be perduring? couldn't you be perduring? couldn't he be perduring? couldn't we be perduring? couldn't you be perduring? couldn't they be perduring?
Perfect
couldn't I have perdured? couldn't you have perdured? couldn't he have perdured? couldn't we have perdured? couldn't you have perdured? couldn't they have perdured?
V-ing perfect
couldn't I have been perduring? couldn't you have been perduring? couldn't he have been perduring? couldn't we have been perduring? couldn't you have been perduring? couldn't they have been perduring?