English verb conjugation
COULD YACK

Regular verb: yack - yacked - yacked

Affirmation

Simple form	V-ing form
I could yack you could yack he could yack we could yack you could yack they could yack	I could be yacking you could be yacking he could be yacking we could be yacking you could be yacking they could be yacking
Perfect	V-ing perfect
I could have yacked you could have yacked he could have yacked we could have yacked you could have yacked they could have yacked	I could have been yacking you could have been yacking he could have been yacking we could have been yacking you could have been yacking they could have been yacking

Negation

Simple form	V-ing form
I could not yack you could not yack he could not yack we could not yack you could not yack they could not yack	I could not be yacking you could not be yacking he could not be yacking we could not be yacking you could not be yacking they could not be yacking
Perfect	V-ing perfect
I could not have yacked you could not have yacked he could not have yacked we could not have yacked you could not have yacked they could not have yacked	I could not have been yacking you could not have been yacking he could not have been yacking we could not have been yacking you could not have been yacking they could not have been yacking

Interrogative form

Simple form	V-ing form
could I yack? could you yack? could he yack? could we yack? could you yack? could they yack?	could I be yacking? could you be yacking? could he be yacking? could we be yacking? could you be yacking? could they be yacking?
Perfect	V-ing perfect
could I have yacked? could you have yacked? could he have yacked? could we have yacked? could you have yacked? could they have yacked?	could I have been yacking? could you have been yacking? could he have been yacking? could we have been yacking? could you have been yacking? could they have been yacking?

Interro-negative form

Simple form	V-ing form
could I not yack? could you not yack? could he not yack? could we not yack? could you not yack? could they not yack?	could I not be yacking? could you not be yacking? could he not be yacking? could we not be yacking? could you not be yacking? could they not be yacking?
Perfect	V-ing perfect
could I not have yacked? could you not have yacked? could he not have yacked? could we not have yacked? could you not have yacked? could they not have yacked?	could I not have been yacking? could you not have been yacking? could he not have been yacking? could we not have been yacking? could you not have been yacking? could they not have been yacking?