must decrease
Regular verb: decrease - decreased- decreased

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must decrease
you must decrease
he must decrease
we must decrease
you must decrease
they must decrease 	I must be decreasing
you must be decreasing
he must be decreasing
we must be decreasing
you must be decreasing
they must be decreasing	I must have decreased
you must have decreased
he must have decreased
we must have decreased
you must have decreased
they must have decreased	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 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't decrease
you mustn't decrease
he mustn't decrease
we mustn't decrease
you mustn't decrease
they mustn't decrease 	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	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	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 	V-ing form 	Perfect 	V-ing perfect 	
must I decrease?
must you decrease?
must he decrease?
must we decrease?
must you decrease?
must they decrease? 	must I be decreasing?
must you be decreasing?
must he be decreasing?
must we be decreasing?
must you be decreasing?
must they be decreasing? 	must I have decreased?
must you have decreased?
must he have decreased?
must we have decreased?
must you have decreased?
must they have decreased? 	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 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I decrease?
mustn't you decrease?
mustn't he decrease?
mustn't we decrease?
mustn't you decrease?
mustn't they decrease? 	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? 	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? 	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?