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