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 couldn't excuse you couldn't excuse she couldn't excuse we couldn't excuse you couldn't excuse they couldn't excuse
V-ing form
I couldn't be excusing you couldn't be excusing she couldn't be excusing we couldn't be excusing you couldn't be excusing they couldn't be excusing
Perfect
I couldn't have excused you couldn't have excused she couldn't have excused we couldn't have excused you couldn't have excused they couldn't have excused
V-ing perfect
I couldn't have been excusing you couldn't have been excusing she couldn't have been excusing we couldn't have been excusing you couldn't have been excusing they couldn't 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
couldn't I excuse? couldn't you excuse? couldn't she excuse? couldn't we excuse? couldn't you excuse? couldn't they excuse?
V-ing form
couldn't I be excusing? couldn't you be excusing? couldn't she be excusing? couldn't we be excusing? couldn't you be excusing? couldn't they be excusing?
Perfect
couldn't I have excused? couldn't you have excused? couldn't she have excused? couldn't we have excused? couldn't you have excused? couldn't they have excused?
V-ing perfect
couldn't I have been excusing? couldn't you have been excusing? couldn't she have been excusing? couldn't we have been excusing? couldn't you have been excusing? couldn't they have been excusing?