I could unbutton you could unbutton he could unbutton we could unbutton you could unbutton they could unbutton
V-ing form
I could be unbuttoning you could be unbuttoning he could be unbuttoning we could be unbuttoning you could be unbuttoning they could be unbuttoning
Perfect
I could have unbuttoned you could have unbuttoned he could have unbuttoned we could have unbuttoned you could have unbuttoned they could have unbuttoned
V-ing perfect
I could have been unbuttoning you could have been unbuttoning he could have been unbuttoning we could have been unbuttoning you could have been unbuttoning they could have been unbuttoning
Negation
Simple form
I could not unbutton you could not unbutton he could not unbutton we could not unbutton you could not unbutton they could not unbutton
V-ing form
I could not be unbuttoning you could not be unbuttoning he could not be unbuttoning we could not be unbuttoning you could not be unbuttoning they could not be unbuttoning
Perfect
I could not have unbuttoned you could not have unbuttoned he could not have unbuttoned we could not have unbuttoned you could not have unbuttoned they could not have unbuttoned
V-ing perfect
I could not have been unbuttoning you could not have been unbuttoning he could not have been unbuttoning we could not have been unbuttoning you could not have been unbuttoning they could not have been unbuttoning
Interrogative form
Simple form
could I unbutton? could you unbutton? could he unbutton? could we unbutton? could you unbutton? could they unbutton?
V-ing form
could I be unbuttoning? could you be unbuttoning? could he be unbuttoning? could we be unbuttoning? could you be unbuttoning? could they be unbuttoning?
Perfect
could I have unbuttoned? could you have unbuttoned? could he have unbuttoned? could we have unbuttoned? could you have unbuttoned? could they have unbuttoned?
V-ing perfect
could I have been unbuttoning? could you have been unbuttoning? could he have been unbuttoning? could we have been unbuttoning? could you have been unbuttoning? could they have been unbuttoning?
Interro-negative form
Simple form
could I not unbutton? could you not unbutton? could he not unbutton? could we not unbutton? could you not unbutton? could they not unbutton?
V-ing form
could I not be unbuttoning? could you not be unbuttoning? could he not be unbuttoning? could we not be unbuttoning? could you not be unbuttoning? could they not be unbuttoning?
Perfect
could I not have unbuttoned? could you not have unbuttoned? could he not have unbuttoned? could we not have unbuttoned? could you not have unbuttoned? could they not have unbuttoned?
V-ing perfect
could I not have been unbuttoning? could you not have been unbuttoning? could he not have been unbuttoning? could we not have been unbuttoning? could you not have been unbuttoning? could they not have been unbuttoning?