could unbutton
Regular verb: unbutton - unbuttoned- unbuttoned

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could unbutton
you could unbutton
he could unbutton
we could unbutton
you could unbutton
they could unbutton 	I could be unbuttoning
you could be unbuttoning
he could be unbuttoning
we could be unbuttoning
you could be unbuttoning
they could be unbuttoning	I could have unbuttoned
you could have unbuttoned
he could have unbuttoned
we could have unbuttoned
you could have unbuttoned
they could have unbuttoned	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 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't unbutton
you couldn't unbutton
he couldn't unbutton
we couldn't unbutton
you couldn't unbutton
they couldn't unbutton 	I couldn't be unbuttoning
you couldn't be unbuttoning
he couldn't be unbuttoning
we couldn't be unbuttoning
you couldn't be unbuttoning
they couldn't be unbuttoning	I couldn't have unbuttoned
you couldn't have unbuttoned
he couldn't have unbuttoned
we couldn't have unbuttoned
you couldn't have unbuttoned
they couldn't have unbuttoned	I couldn't have been unbuttoning
you couldn't have been unbuttoning
he couldn't have been unbuttoning
we couldn't have been unbuttoning
you couldn't have been unbuttoning
they couldn't have been unbuttoning	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I unbutton?
could you unbutton?
could he unbutton?
could we unbutton?
could you unbutton?
could they unbutton? 	could I be unbuttoning?
could you be unbuttoning?
could he be unbuttoning?
could we be unbuttoning?
could you be unbuttoning?
could they be unbuttoning? 	could I have unbuttoned?
could you have unbuttoned?
could he have unbuttoned?
could we have unbuttoned?
could you have unbuttoned?
could they have unbuttoned? 	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 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I unbutton?
couldn't you unbutton?
couldn't he unbutton?
couldn't we unbutton?
couldn't you unbutton?
couldn't they unbutton? 	couldn't I be unbuttoning?
couldn't you be unbuttoning?
couldn't he be unbuttoning?
couldn't we be unbuttoning?
couldn't you be unbuttoning?
couldn't they be unbuttoning? 	couldn't I have unbuttoned?
couldn't you have unbuttoned?
couldn't he have unbuttoned?
couldn't we have unbuttoned?
couldn't you have unbuttoned?
couldn't they have unbuttoned? 	couldn't I have been unbuttoning?
couldn't you have been unbuttoning?
couldn't he have been unbuttoning?
couldn't we have been unbuttoning?
couldn't you have been unbuttoning?
couldn't they have been unbuttoning?