I could step you could step he could step we could step you could step they could step
V-ing form
I could be stepping you could be stepping he could be stepping we could be stepping you could be stepping they could be stepping
Perfect
I could have stepped you could have stepped he could have stepped we could have stepped you could have stepped they could have stepped
V-ing perfect
I could have been stepping you could have been stepping he could have been stepping we could have been stepping you could have been stepping they could have been stepping
Negation
Simple form
I could not step you could not step he could not step we could not step you could not step they could not step
V-ing form
I could not be stepping you could not be stepping he could not be stepping we could not be stepping you could not be stepping they could not be stepping
Perfect
I could not have stepped you could not have stepped he could not have stepped we could not have stepped you could not have stepped they could not have stepped
V-ing perfect
I could not have been stepping you could not have been stepping he could not have been stepping we could not have been stepping you could not have been stepping they could not have been stepping
Interrogative form
Simple form
could I step? could you step? could he step? could we step? could you step? could they step?
V-ing form
could I be stepping? could you be stepping? could he be stepping? could we be stepping? could you be stepping? could they be stepping?
Perfect
could I have stepped? could you have stepped? could he have stepped? could we have stepped? could you have stepped? could they have stepped?
V-ing perfect
could I have been stepping? could you have been stepping? could he have been stepping? could we have been stepping? could you have been stepping? could they have been stepping?
Interro-negative form
Simple form
could I not step? could you not step? could he not step? could we not step? could you not step? could they not step?
V-ing form
could I not be stepping? could you not be stepping? could he not be stepping? could we not be stepping? could you not be stepping? could they not be stepping?
Perfect
could I not have stepped? could you not have stepped? could he not have stepped? could we not have stepped? could you not have stepped? could they not have stepped?
V-ing perfect
could I not have been stepping? could you not have been stepping? could he not have been stepping? could we not have been stepping? could you not have been stepping? could they not have been stepping?