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