I could whiten you could whiten she could whiten we could whiten you could whiten they could whiten
V-ing form
I could be whitening you could be whitening she could be whitening we could be whitening you could be whitening they could be whitening
Perfect
I could have whitened you could have whitened she could have whitened we could have whitened you could have whitened they could have whitened
V-ing perfect
I could have been whitening you could have been whitening she could have been whitening we could have been whitening you could have been whitening they could have been whitening
Negation
Simple form
I could not whiten you could not whiten she could not whiten we could not whiten you could not whiten they could not whiten
V-ing form
I could not be whitening you could not be whitening she could not be whitening we could not be whitening you could not be whitening they could not be whitening
Perfect
I could not have whitened you could not have whitened she could not have whitened we could not have whitened you could not have whitened they could not have whitened
V-ing perfect
I could not have been whitening you could not have been whitening she could not have been whitening we could not have been whitening you could not have been whitening they could not have been whitening
Interrogative form
Simple form
could I whiten? could you whiten? could she whiten? could we whiten? could you whiten? could they whiten?
V-ing form
could I be whitening? could you be whitening? could she be whitening? could we be whitening? could you be whitening? could they be whitening?
Perfect
could I have whitened? could you have whitened? could she have whitened? could we have whitened? could you have whitened? could they have whitened?
V-ing perfect
could I have been whitening? could you have been whitening? could she have been whitening? could we have been whitening? could you have been whitening? could they have been whitening?
Interro-negative form
Simple form
could I not whiten? could you not whiten? could she not whiten? could we not whiten? could you not whiten? could they not whiten?
V-ing form
could I not be whitening? could you not be whitening? could she not be whitening? could we not be whitening? could you not be whitening? could they not be whitening?
Perfect
could I not have whitened? could you not have whitened? could she not have whitened? could we not have whitened? could you not have whitened? could they not have whitened?
V-ing perfect
could I not have been whitening? could you not have been whitening? could she not have been whitening? could we not have been whitening? could you not have been whitening? could they not have been whitening?