I could excuse you could excuse she could excuse we could excuse you could excuse they could excuse
V-ing form
I could be excusing you could be excusing she could be excusing we could be excusing you could be excusing they could be excusing
Perfect
I could have excused you could have excused she could have excused we could have excused you could have excused they could have excused
V-ing perfect
I could have been excusing you could have been excusing she could have been excusing we could have been excusing you could have been excusing they could have been excusing
Negation
Simple form
I could not excuse you could not excuse she could not excuse we could not excuse you could not excuse they could not excuse
V-ing form
I could not be excusing you could not be excusing she could not be excusing we could not be excusing you could not be excusing they could not be excusing
Perfect
I could not have excused you could not have excused she could not have excused we could not have excused you could not have excused they could not have excused
V-ing perfect
I could not have been excusing you could not have been excusing she could not have been excusing we could not have been excusing you could not have been excusing they could not have been excusing
Interrogative form
Simple form
could I excuse? could you excuse? could she excuse? could we excuse? could you excuse? could they excuse?
V-ing form
could I be excusing? could you be excusing? could she be excusing? could we be excusing? could you be excusing? could they be excusing?
Perfect
could I have excused? could you have excused? could she have excused? could we have excused? could you have excused? could they have excused?
V-ing perfect
could I have been excusing? could you have been excusing? could she have been excusing? could we have been excusing? could you have been excusing? could they have been excusing?
Interro-negative form
Simple form
could I not excuse? could you not excuse? could she not excuse? could we not excuse? could you not excuse? could they not excuse?
V-ing form
could I not be excusing? could you not be excusing? could she not be excusing? could we not be excusing? could you not be excusing? could they not be excusing?
Perfect
could I not have excused? could you not have excused? could she not have excused? could we not have excused? could you not have excused? could they not have excused?
V-ing perfect
could I not have been excusing? could you not have been excusing? could she not have been excusing? could we not have been excusing? could you not have been excusing? could they not have been excusing?