I could burble you could burble he could burble we could burble you could burble they could burble
V-ing form
I could be burbling you could be burbling he could be burbling we could be burbling you could be burbling they could be burbling
Perfect
I could have burbled you could have burbled he could have burbled we could have burbled you could have burbled they could have burbled
V-ing perfect
I could have been burbling you could have been burbling he could have been burbling we could have been burbling you could have been burbling they could have been burbling
Negation
Simple form
I could not burble you could not burble he could not burble we could not burble you could not burble they could not burble
V-ing form
I could not be burbling you could not be burbling he could not be burbling we could not be burbling you could not be burbling they could not be burbling
Perfect
I could not have burbled you could not have burbled he could not have burbled we could not have burbled you could not have burbled they could not have burbled
V-ing perfect
I could not have been burbling you could not have been burbling he could not have been burbling we could not have been burbling you could not have been burbling they could not have been burbling
Interrogative form
Simple form
could I burble? could you burble? could he burble? could we burble? could you burble? could they burble?
V-ing form
could I be burbling? could you be burbling? could he be burbling? could we be burbling? could you be burbling? could they be burbling?
Perfect
could I have burbled? could you have burbled? could he have burbled? could we have burbled? could you have burbled? could they have burbled?
V-ing perfect
could I have been burbling? could you have been burbling? could he have been burbling? could we have been burbling? could you have been burbling? could they have been burbling?
Interro-negative form
Simple form
could I not burble? could you not burble? could he not burble? could we not burble? could you not burble? could they not burble?
V-ing form
could I not be burbling? could you not be burbling? could he not be burbling? could we not be burbling? could you not be burbling? could they not be burbling?
Perfect
could I not have burbled? could you not have burbled? could he not have burbled? could we not have burbled? could you not have burbled? could they not have burbled?
V-ing perfect
could I not have been burbling? could you not have been burbling? could he not have been burbling? could we not have been burbling? could you not have been burbling? could they not have been burbling?