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