I could diphthongize you could diphthongize she could diphthongize we could diphthongize you could diphthongize they could diphthongize
V-ing form
I could be diphthongizing you could be diphthongizing she could be diphthongizing we could be diphthongizing you could be diphthongizing they could be diphthongizing
Perfect
I could have diphthongized you could have diphthongized she could have diphthongized we could have diphthongized you could have diphthongized they could have diphthongized
V-ing perfect
I could have been diphthongizing you could have been diphthongizing she could have been diphthongizing we could have been diphthongizing you could have been diphthongizing they could have been diphthongizing
Negation
Simple form
I could not diphthongize you could not diphthongize she could not diphthongize we could not diphthongize you could not diphthongize they could not diphthongize
V-ing form
I could not be diphthongizing you could not be diphthongizing she could not be diphthongizing we could not be diphthongizing you could not be diphthongizing they could not be diphthongizing
Perfect
I could not have diphthongized you could not have diphthongized she could not have diphthongized we could not have diphthongized you could not have diphthongized they could not have diphthongized
V-ing perfect
I could not have been diphthongizing you could not have been diphthongizing she could not have been diphthongizing we could not have been diphthongizing you could not have been diphthongizing they could not have been diphthongizing
Interrogative form
Simple form
could I diphthongize? could you diphthongize? could she diphthongize? could we diphthongize? could you diphthongize? could they diphthongize?
V-ing form
could I be diphthongizing? could you be diphthongizing? could she be diphthongizing? could we be diphthongizing? could you be diphthongizing? could they be diphthongizing?
Perfect
could I have diphthongized? could you have diphthongized? could she have diphthongized? could we have diphthongized? could you have diphthongized? could they have diphthongized?
V-ing perfect
could I have been diphthongizing? could you have been diphthongizing? could she have been diphthongizing? could we have been diphthongizing? could you have been diphthongizing? could they have been diphthongizing?
Interro-negative form
Simple form
could I not diphthongize? could you not diphthongize? could she not diphthongize? could we not diphthongize? could you not diphthongize? could they not diphthongize?
V-ing form
could I not be diphthongizing? could you not be diphthongizing? could she not be diphthongizing? could we not be diphthongizing? could you not be diphthongizing? could they not be diphthongizing?
Perfect
could I not have diphthongized? could you not have diphthongized? could she not have diphthongized? could we not have diphthongized? could you not have diphthongized? could they not have diphthongized?
V-ing perfect
could I not have been diphthongizing? could you not have been diphthongizing? could she not have been diphthongizing? could we not have been diphthongizing? could you not have been diphthongizing? could they not have been diphthongizing?