I could diphthongise you could diphthongise she could diphthongise we could diphthongise you could diphthongise they could diphthongise
V-ing form
I could be diphthongising you could be diphthongising she could be diphthongising we could be diphthongising you could be diphthongising they could be diphthongising
Perfect
I could have diphthongised you could have diphthongised she could have diphthongised we could have diphthongised you could have diphthongised they could have diphthongised
V-ing perfect
I could have been diphthongising you could have been diphthongising she could have been diphthongising we could have been diphthongising you could have been diphthongising they could have been diphthongising
Negation
Simple form
I couldn't diphthongise you couldn't diphthongise she couldn't diphthongise we couldn't diphthongise you couldn't diphthongise they couldn't diphthongise
V-ing form
I couldn't be diphthongising you couldn't be diphthongising she couldn't be diphthongising we couldn't be diphthongising you couldn't be diphthongising they couldn't be diphthongising
Perfect
I couldn't have diphthongised you couldn't have diphthongised she couldn't have diphthongised we couldn't have diphthongised you couldn't have diphthongised they couldn't have diphthongised
V-ing perfect
I couldn't have been diphthongising you couldn't have been diphthongising she couldn't have been diphthongising we couldn't have been diphthongising you couldn't have been diphthongising they couldn't have been diphthongising
Interrogative form
Simple form
could I diphthongise? could you diphthongise? could she diphthongise? could we diphthongise? could you diphthongise? could they diphthongise?
V-ing form
could I be diphthongising? could you be diphthongising? could she be diphthongising? could we be diphthongising? could you be diphthongising? could they be diphthongising?
Perfect
could I have diphthongised? could you have diphthongised? could she have diphthongised? could we have diphthongised? could you have diphthongised? could they have diphthongised?
V-ing perfect
could I have been diphthongising? could you have been diphthongising? could she have been diphthongising? could we have been diphthongising? could you have been diphthongising? could they have been diphthongising?
Interro-negative form
Simple form
couldn't I diphthongise? couldn't you diphthongise? couldn't she diphthongise? couldn't we diphthongise? couldn't you diphthongise? couldn't they diphthongise?
V-ing form
couldn't I be diphthongising? couldn't you be diphthongising? couldn't she be diphthongising? couldn't we be diphthongising? couldn't you be diphthongising? couldn't they be diphthongising?
Perfect
couldn't I have diphthongised? couldn't you have diphthongised? couldn't she have diphthongised? couldn't we have diphthongised? couldn't you have diphthongised? couldn't they have diphthongised?
V-ing perfect
couldn't I have been diphthongising? couldn't you have been diphthongising? couldn't she have been diphthongising? couldn't we have been diphthongising? couldn't you have been diphthongising? couldn't they have been diphthongising?