I could slip you could slip he could slip we could slip you could slip they could slip
V-ing form
I could be slipping you could be slipping he could be slipping we could be slipping you could be slipping they could be slipping
Perfect
I could have slipped you could have slipped he could have slipped we could have slipped you could have slipped they could have slipped
V-ing perfect
I could have been slipping you could have been slipping he could have been slipping we could have been slipping you could have been slipping they could have been slipping
Negation
Simple form
I could not slip you could not slip he could not slip we could not slip you could not slip they could not slip
V-ing form
I could not be slipping you could not be slipping he could not be slipping we could not be slipping you could not be slipping they could not be slipping
Perfect
I could not have slipped you could not have slipped he could not have slipped we could not have slipped you could not have slipped they could not have slipped
V-ing perfect
I could not have been slipping you could not have been slipping he could not have been slipping we could not have been slipping you could not have been slipping they could not have been slipping
Interrogative form
Simple form
could I slip? could you slip? could he slip? could we slip? could you slip? could they slip?
V-ing form
could I be slipping? could you be slipping? could he be slipping? could we be slipping? could you be slipping? could they be slipping?
Perfect
could I have slipped? could you have slipped? could he have slipped? could we have slipped? could you have slipped? could they have slipped?
V-ing perfect
could I have been slipping? could you have been slipping? could he have been slipping? could we have been slipping? could you have been slipping? could they have been slipping?
Interro-negative form
Simple form
could I not slip? could you not slip? could he not slip? could we not slip? could you not slip? could they not slip?
V-ing form
could I not be slipping? could you not be slipping? could he not be slipping? could we not be slipping? could you not be slipping? could they not be slipping?
Perfect
could I not have slipped? could you not have slipped? could he not have slipped? could we not have slipped? could you not have slipped? could they not have slipped?
V-ing perfect
could I not have been slipping? could you not have been slipping? could he not have been slipping? could we not have been slipping? could you not have been slipping? could they not have been slipping?