I could revise you could revise he could revise we could revise you could revise they could revise
V-ing form
I could be revising you could be revising he could be revising we could be revising you could be revising they could be revising
Perfect
I could have revised you could have revised he could have revised we could have revised you could have revised they could have revised
V-ing perfect
I could have been revising you could have been revising he could have been revising we could have been revising you could have been revising they could have been revising
Negation
Simple form
I could not revise you could not revise he could not revise we could not revise you could not revise they could not revise
V-ing form
I could not be revising you could not be revising he could not be revising we could not be revising you could not be revising they could not be revising
Perfect
I could not have revised you could not have revised he could not have revised we could not have revised you could not have revised they could not have revised
V-ing perfect
I could not have been revising you could not have been revising he could not have been revising we could not have been revising you could not have been revising they could not have been revising
Interrogative form
Simple form
could I revise? could you revise? could he revise? could we revise? could you revise? could they revise?
V-ing form
could I be revising? could you be revising? could he be revising? could we be revising? could you be revising? could they be revising?
Perfect
could I have revised? could you have revised? could he have revised? could we have revised? could you have revised? could they have revised?
V-ing perfect
could I have been revising? could you have been revising? could he have been revising? could we have been revising? could you have been revising? could they have been revising?
Interro-negative form
Simple form
could I not revise? could you not revise? could he not revise? could we not revise? could you not revise? could they not revise?
V-ing form
could I not be revising? could you not be revising? could he not be revising? could we not be revising? could you not be revising? could they not be revising?
Perfect
could I not have revised? could you not have revised? could he not have revised? could we not have revised? could you not have revised? could they not have revised?
V-ing perfect
could I not have been revising? could you not have been revising? could he not have been revising? could we not have been revising? could you not have been revising? could they not have been revising?