must ascertain
Regular verb: ascertain - ascertained- ascertained

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must ascertain
you must ascertain
she must ascertain
we must ascertain
you must ascertain
they must ascertain 	I must be ascertaining
you must be ascertaining
she must be ascertaining
we must be ascertaining
you must be ascertaining
they must be ascertaining	I must have ascertained
you must have ascertained
she must have ascertained
we must have ascertained
you must have ascertained
they must have ascertained	I must have been ascertaining
you must have been ascertaining
she must have been ascertaining
we must have been ascertaining
you must have been ascertaining
they must have been ascertaining	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't ascertain
you mustn't ascertain
she mustn't ascertain
we mustn't ascertain
you mustn't ascertain
they mustn't ascertain 	I mustn't be ascertaining
you mustn't be ascertaining
she mustn't be ascertaining
we mustn't be ascertaining
you mustn't be ascertaining
they mustn't be ascertaining	I mustn't have ascertained
you mustn't have ascertained
she mustn't have ascertained
we mustn't have ascertained
you mustn't have ascertained
they mustn't have ascertained	I mustn't have been ascertaining
you mustn't have been ascertaining
she mustn't have been ascertaining
we mustn't have been ascertaining
you mustn't have been ascertaining
they mustn't have been ascertaining	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I ascertain?
must you ascertain?
must she ascertain?
must we ascertain?
must you ascertain?
must they ascertain? 	must I be ascertaining?
must you be ascertaining?
must she be ascertaining?
must we be ascertaining?
must you be ascertaining?
must they be ascertaining? 	must I have ascertained?
must you have ascertained?
must she have ascertained?
must we have ascertained?
must you have ascertained?
must they have ascertained? 	must I have been ascertaining?
must you have been ascertaining?
must she have been ascertaining?
must we have been ascertaining?
must you have been ascertaining?
must they have been ascertaining? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I ascertain?
mustn't you ascertain?
mustn't she ascertain?
mustn't we ascertain?
mustn't you ascertain?
mustn't they ascertain? 	mustn't I be ascertaining?
mustn't you be ascertaining?
mustn't she be ascertaining?
mustn't we be ascertaining?
mustn't you be ascertaining?
mustn't they be ascertaining? 	mustn't I have ascertained?
mustn't you have ascertained?
mustn't she have ascertained?
mustn't we have ascertained?
mustn't you have ascertained?
mustn't they have ascertained? 	mustn't I have been ascertaining?
mustn't you have been ascertaining?
mustn't she have been ascertaining?
mustn't we have been ascertaining?
mustn't you have been ascertaining?
mustn't they have been ascertaining?