I could revise you could revise she could revise we could revise you could revise they could revise
V-ing form
I could be revising you could be revising she could be revising we could be revising you could be revising they could be revising
Perfect
I could have revised you could have revised she 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 she could have been revising we could have been revising you could have been revising they could have been revising
Negation
Simple form
I couldn't revise you couldn't revise she couldn't revise we couldn't revise you couldn't revise they couldn't revise
V-ing form
I couldn't be revising you couldn't be revising she couldn't be revising we couldn't be revising you couldn't be revising they couldn't be revising
Perfect
I couldn't have revised you couldn't have revised she couldn't have revised we couldn't have revised you couldn't have revised they couldn't have revised
V-ing perfect
I couldn't have been revising you couldn't have been revising she couldn't have been revising we couldn't have been revising you couldn't have been revising they couldn't have been revising
Interrogative form
Simple form
could I revise? could you revise? could she revise? could we revise? could you revise? could they revise?
V-ing form
could I be revising? could you be revising? could she be revising? could we be revising? could you be revising? could they be revising?
Perfect
could I have revised? could you have revised? could she 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 she have been revising? could we have been revising? could you have been revising? could they have been revising?
Interro-negative form
Simple form
couldn't I revise? couldn't you revise? couldn't she revise? couldn't we revise? couldn't you revise? couldn't they revise?
V-ing form
couldn't I be revising? couldn't you be revising? couldn't she be revising? couldn't we be revising? couldn't you be revising? couldn't they be revising?
Perfect
couldn't I have revised? couldn't you have revised? couldn't she have revised? couldn't we have revised? couldn't you have revised? couldn't they have revised?
V-ing perfect
couldn't I have been revising? couldn't you have been revising? couldn't she have been revising? couldn't we have been revising? couldn't you have been revising? couldn't they have been revising?