I must regress you must regress he must regress we must regress you must regress they must regress
V-ing form
I must be regressing you must be regressing he must be regressing we must be regressing you must be regressing they must be regressing
Perfect
I must have regressed you must have regressed he must have regressed we must have regressed you must have regressed they must have regressed
V-ing perfect
I must have been regressing you must have been regressing he must have been regressing we must have been regressing you must have been regressing they must have been regressing
Negation
Simple form
I mustn't regress you mustn't regress he mustn't regress we mustn't regress you mustn't regress they mustn't regress
V-ing form
I mustn't be regressing you mustn't be regressing he mustn't be regressing we mustn't be regressing you mustn't be regressing they mustn't be regressing
Perfect
I mustn't have regressed you mustn't have regressed he mustn't have regressed we mustn't have regressed you mustn't have regressed they mustn't have regressed
V-ing perfect
I mustn't have been regressing you mustn't have been regressing he mustn't have been regressing we mustn't have been regressing you mustn't have been regressing they mustn't have been regressing
Interrogative form
Simple form
must I regress? must you regress? must he regress? must we regress? must you regress? must they regress?
V-ing form
must I be regressing? must you be regressing? must he be regressing? must we be regressing? must you be regressing? must they be regressing?
Perfect
must I have regressed? must you have regressed? must he have regressed? must we have regressed? must you have regressed? must they have regressed?
V-ing perfect
must I have been regressing? must you have been regressing? must he have been regressing? must we have been regressing? must you have been regressing? must they have been regressing?
Interro-negative form
Simple form
mustn't I regress? mustn't you regress? mustn't he regress? mustn't we regress? mustn't you regress? mustn't they regress?
V-ing form
mustn't I be regressing? mustn't you be regressing? mustn't he be regressing? mustn't we be regressing? mustn't you be regressing? mustn't they be regressing?
Perfect
mustn't I have regressed? mustn't you have regressed? mustn't he have regressed? mustn't we have regressed? mustn't you have regressed? mustn't they have regressed?
V-ing perfect
mustn't I have been regressing? mustn't you have been regressing? mustn't he have been regressing? mustn't we have been regressing? mustn't you have been regressing? mustn't they have been regressing?