I could comb you could comb he could comb we could comb you could comb they could comb
V-ing form
I could be combing you could be combing he could be combing we could be combing you could be combing they could be combing
Perfect
I could have combed you could have combed he could have combed we could have combed you could have combed they could have combed
V-ing perfect
I could have been combing you could have been combing he could have been combing we could have been combing you could have been combing they could have been combing
Negation
Simple form
I couldn't comb you couldn't comb he couldn't comb we couldn't comb you couldn't comb they couldn't comb
V-ing form
I couldn't be combing you couldn't be combing he couldn't be combing we couldn't be combing you couldn't be combing they couldn't be combing
Perfect
I couldn't have combed you couldn't have combed he couldn't have combed we couldn't have combed you couldn't have combed they couldn't have combed
V-ing perfect
I couldn't have been combing you couldn't have been combing he couldn't have been combing we couldn't have been combing you couldn't have been combing they couldn't have been combing
Interrogative form
Simple form
could I comb? could you comb? could he comb? could we comb? could you comb? could they comb?
V-ing form
could I be combing? could you be combing? could he be combing? could we be combing? could you be combing? could they be combing?
Perfect
could I have combed? could you have combed? could he have combed? could we have combed? could you have combed? could they have combed?
V-ing perfect
could I have been combing? could you have been combing? could he have been combing? could we have been combing? could you have been combing? could they have been combing?
Interro-negative form
Simple form
couldn't I comb? couldn't you comb? couldn't he comb? couldn't we comb? couldn't you comb? couldn't they comb?
V-ing form
couldn't I be combing? couldn't you be combing? couldn't he be combing? couldn't we be combing? couldn't you be combing? couldn't they be combing?
Perfect
couldn't I have combed? couldn't you have combed? couldn't he have combed? couldn't we have combed? couldn't you have combed? couldn't they have combed?
V-ing perfect
couldn't I have been combing? couldn't you have been combing? couldn't he have been combing? couldn't we have been combing? couldn't you have been combing? couldn't they have been combing?