must doubt
Regular verb: doubt - doubted- doubted

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must doubt
you must doubt
she must doubt
we must doubt
you must doubt
they must doubt 	I must be doubting
you must be doubting
she must be doubting
we must be doubting
you must be doubting
they must be doubting	I must have doubted
you must have doubted
she must have doubted
we must have doubted
you must have doubted
they must have doubted	I must have been doubting
you must have been doubting
she must have been doubting
we must have been doubting
you must have been doubting
they must have been doubting	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't doubt
you mustn't doubt
she mustn't doubt
we mustn't doubt
you mustn't doubt
they mustn't doubt 	I mustn't be doubting
you mustn't be doubting
she mustn't be doubting
we mustn't be doubting
you mustn't be doubting
they mustn't be doubting	I mustn't have doubted
you mustn't have doubted
she mustn't have doubted
we mustn't have doubted
you mustn't have doubted
they mustn't have doubted	I mustn't have been doubting
you mustn't have been doubting
she mustn't have been doubting
we mustn't have been doubting
you mustn't have been doubting
they mustn't have been doubting	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I doubt?
must you doubt?
must she doubt?
must we doubt?
must you doubt?
must they doubt? 	must I be doubting?
must you be doubting?
must she be doubting?
must we be doubting?
must you be doubting?
must they be doubting? 	must I have doubted?
must you have doubted?
must she have doubted?
must we have doubted?
must you have doubted?
must they have doubted? 	must I have been doubting?
must you have been doubting?
must she have been doubting?
must we have been doubting?
must you have been doubting?
must they have been doubting? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I doubt?
mustn't you doubt?
mustn't she doubt?
mustn't we doubt?
mustn't you doubt?
mustn't they doubt? 	mustn't I be doubting?
mustn't you be doubting?
mustn't she be doubting?
mustn't we be doubting?
mustn't you be doubting?
mustn't they be doubting? 	mustn't I have doubted?
mustn't you have doubted?
mustn't she have doubted?
mustn't we have doubted?
mustn't you have doubted?
mustn't they have doubted? 	mustn't I have been doubting?
mustn't you have been doubting?
mustn't she have been doubting?
mustn't we have been doubting?
mustn't you have been doubting?
mustn't they have been doubting?