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