English verb conjugation
COULD QUACK

Regular verb: quack - quacked - quacked

Affirmation

Simple form	V-ing form
I could quack you could quack he could quack we could quack you could quack they could quack	I could be quacking you could be quacking he could be quacking we could be quacking you could be quacking they could be quacking
Perfect	V-ing perfect
I could have quacked you could have quacked he could have quacked we could have quacked you could have quacked they could have quacked	I could have been quacking you could have been quacking he could have been quacking we could have been quacking you could have been quacking they could have been quacking

Negation

Simple form	V-ing form
I could not quack you could not quack he could not quack we could not quack you could not quack they could not quack	I could not be quacking you could not be quacking he could not be quacking we could not be quacking you could not be quacking they could not be quacking
Perfect	V-ing perfect
I could not have quacked you could not have quacked he could not have quacked we could not have quacked you could not have quacked they could not have quacked	I could not have been quacking you could not have been quacking he could not have been quacking we could not have been quacking you could not have been quacking they could not have been quacking

Interrogative form

Simple form	V-ing form
could I quack? could you quack? could he quack? could we quack? could you quack? could they quack?	could I be quacking? could you be quacking? could he be quacking? could we be quacking? could you be quacking? could they be quacking?
Perfect	V-ing perfect
could I have quacked? could you have quacked? could he have quacked? could we have quacked? could you have quacked? could they have quacked?	could I have been quacking? could you have been quacking? could he have been quacking? could we have been quacking? could you have been quacking? could they have been quacking?

Interro-negative form

Simple form	V-ing form
could I not quack? could you not quack? could he not quack? could we not quack? could you not quack? could they not quack?	could I not be quacking? could you not be quacking? could he not be quacking? could we not be quacking? could you not be quacking? could they not be quacking?
Perfect	V-ing perfect
could I not have quacked? could you not have quacked? could he not have quacked? could we not have quacked? could you not have quacked? could they not have quacked?	could I not have been quacking? could you not have been quacking? could he not have been quacking? could we not have been quacking? could you not have been quacking? could they not have been quacking?