I could march you could march he could march we could march you could march they could march
V-ing form
I could be marching you could be marching he could be marching we could be marching you could be marching they could be marching
Perfect
I could have marched you could have marched he could have marched we could have marched you could have marched they could have marched
V-ing perfect
I could have been marching you could have been marching he could have been marching we could have been marching you could have been marching they could have been marching
Negation
Simple form
I could not march you could not march he could not march we could not march you could not march they could not march
V-ing form
I could not be marching you could not be marching he could not be marching we could not be marching you could not be marching they could not be marching
Perfect
I could not have marched you could not have marched he could not have marched we could not have marched you could not have marched they could not have marched
V-ing perfect
I could not have been marching you could not have been marching he could not have been marching we could not have been marching you could not have been marching they could not have been marching
Interrogative form
Simple form
could I march? could you march? could he march? could we march? could you march? could they march?
V-ing form
could I be marching? could you be marching? could he be marching? could we be marching? could you be marching? could they be marching?
Perfect
could I have marched? could you have marched? could he have marched? could we have marched? could you have marched? could they have marched?
V-ing perfect
could I have been marching? could you have been marching? could he have been marching? could we have been marching? could you have been marching? could they have been marching?
Interro-negative form
Simple form
could I not march? could you not march? could he not march? could we not march? could you not march? could they not march?
V-ing form
could I not be marching? could you not be marching? could he not be marching? could we not be marching? could you not be marching? could they not be marching?
Perfect
could I not have marched? could you not have marched? could he not have marched? could we not have marched? could you not have marched? could they not have marched?
V-ing perfect
could I not have been marching? could you not have been marching? could he not have been marching? could we not have been marching? could you not have been marching? could they not have been marching?