English verb conjugation
MUST YACK

Regular verb: yack - yacked - yacked

Affirmation

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

Negation

Simple form	V-ing form
I mustn't yack you mustn't yack he mustn't yack we mustn't yack you mustn't yack they mustn't yack	I mustn't be yacking you mustn't be yacking he mustn't be yacking we mustn't be yacking you mustn't be yacking they mustn't be yacking
Perfect	V-ing perfect
I mustn't have yacked you mustn't have yacked he mustn't have yacked we mustn't have yacked you mustn't have yacked they mustn't have yacked	I mustn't have been yacking you mustn't have been yacking he mustn't have been yacking we mustn't have been yacking you mustn't have been yacking they mustn't have been yacking

Interrogative form

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

Interro-negative form

Simple form	V-ing form
mustn't I yack? mustn't you yack? mustn't he yack? mustn't we yack? mustn't you yack? mustn't they yack?	mustn't I be yacking? mustn't you be yacking? mustn't he be yacking? mustn't we be yacking? mustn't you be yacking? mustn't they be yacking?
Perfect	V-ing perfect
mustn't I have yacked? mustn't you have yacked? mustn't he have yacked? mustn't we have yacked? mustn't you have yacked? mustn't they have yacked?	mustn't I have been yacking? mustn't you have been yacking? mustn't he have been yacking? mustn't we have been yacking? mustn't you have been yacking? mustn't they have been yacking?