English verb conjugation
MUST LACK

Regular verb: lack - lacked - lacked

Affirmation

Simple form	V-ing form
I must lack you must lack he must lack we must lack you must lack they must lack	I must be lacking you must be lacking he must be lacking we must be lacking you must be lacking they must be lacking
Perfect	V-ing perfect
I must have lacked you must have lacked he must have lacked we must have lacked you must have lacked they must have lacked	I must have been lacking you must have been lacking he must have been lacking we must have been lacking you must have been lacking they must have been lacking

Negation

Simple form	V-ing form
I mustn't lack you mustn't lack he mustn't lack we mustn't lack you mustn't lack they mustn't lack	I mustn't be lacking you mustn't be lacking he mustn't be lacking we mustn't be lacking you mustn't be lacking they mustn't be lacking
Perfect	V-ing perfect
I mustn't have lacked you mustn't have lacked he mustn't have lacked we mustn't have lacked you mustn't have lacked they mustn't have lacked	I mustn't have been lacking you mustn't have been lacking he mustn't have been lacking we mustn't have been lacking you mustn't have been lacking they mustn't have been lacking

Interrogative form

Simple form	V-ing form
must I lack? must you lack? must he lack? must we lack? must you lack? must they lack?	must I be lacking? must you be lacking? must he be lacking? must we be lacking? must you be lacking? must they be lacking?
Perfect	V-ing perfect
must I have lacked? must you have lacked? must he have lacked? must we have lacked? must you have lacked? must they have lacked?	must I have been lacking? must you have been lacking? must he have been lacking? must we have been lacking? must you have been lacking? must they have been lacking?

Interro-negative form

Simple form	V-ing form
mustn't I lack? mustn't you lack? mustn't he lack? mustn't we lack? mustn't you lack? mustn't they lack?	mustn't I be lacking? mustn't you be lacking? mustn't he be lacking? mustn't we be lacking? mustn't you be lacking? mustn't they be lacking?
Perfect	V-ing perfect
mustn't I have lacked? mustn't you have lacked? mustn't he have lacked? mustn't we have lacked? mustn't you have lacked? mustn't they have lacked?	mustn't I have been lacking? mustn't you have been lacking? mustn't he have been lacking? mustn't we have been lacking? mustn't you have been lacking? mustn't they have been lacking?