I could frog you could frog she could frog we could frog you could frog they could frog
V-ing form
I could be froging you could be froging she could be froging we could be froging you could be froging they could be froging
Perfect
I could have froged you could have froged she could have froged we could have froged you could have froged they could have froged
V-ing perfect
I could have been froging you could have been froging she could have been froging we could have been froging you could have been froging they could have been froging
Negation
Simple form
I could not frog you could not frog she could not frog we could not frog you could not frog they could not frog
V-ing form
I could not be froging you could not be froging she could not be froging we could not be froging you could not be froging they could not be froging
Perfect
I could not have froged you could not have froged she could not have froged we could not have froged you could not have froged they could not have froged
V-ing perfect
I could not have been froging you could not have been froging she could not have been froging we could not have been froging you could not have been froging they could not have been froging
Interrogative form
Simple form
could I frog? could you frog? could she frog? could we frog? could you frog? could they frog?
V-ing form
could I be froging? could you be froging? could she be froging? could we be froging? could you be froging? could they be froging?
Perfect
could I have froged? could you have froged? could she have froged? could we have froged? could you have froged? could they have froged?
V-ing perfect
could I have been froging? could you have been froging? could she have been froging? could we have been froging? could you have been froging? could they have been froging?
Interro-negative form
Simple form
could I not frog? could you not frog? could she not frog? could we not frog? could you not frog? could they not frog?
V-ing form
could I not be froging? could you not be froging? could she not be froging? could we not be froging? could you not be froging? could they not be froging?
Perfect
could I not have froged? could you not have froged? could she not have froged? could we not have froged? could you not have froged? could they not have froged?
V-ing perfect
could I not have been froging? could you not have been froging? could she not have been froging? could we not have been froging? could you not have been froging? could they not have been froging?