I could diphthongize you could diphthongize he could diphthongize we could diphthongize you could diphthongize they could diphthongize
V-ing form
I could be diphthongizing you could be diphthongizing he could be diphthongizing we could be diphthongizing you could be diphthongizing they could be diphthongizing
Perfect
I could have diphthongized you could have diphthongized he 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 he 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 he 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 he 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 he 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 he 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 he diphthongize? could we diphthongize? could you diphthongize? could they diphthongize?
V-ing form
could I be diphthongizing? could you be diphthongizing? could he be diphthongizing? could we be diphthongizing? could you be diphthongizing? could they be diphthongizing?
Perfect
could I have diphthongized? could you have diphthongized? could he 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 he 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 he 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 he 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 he 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 he not have been diphthongizing? could we not have been diphthongizing? could you not have been diphthongizing? could they not have been diphthongizing?