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