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