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