must observe
Regular verb: observe - observed- observed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must observe
you must observe
he must observe
we must observe
you must observe
they must observe 	I must be observing
you must be observing
he must be observing
we must be observing
you must be observing
they must be observing	I must have observed
you must have observed
he must have observed
we must have observed
you must have observed
they must have observed	I must have been observing
you must have been observing
he must have been observing
we must have been observing
you must have been observing
they must have been observing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't observe
you mustn't observe
he mustn't observe
we mustn't observe
you mustn't observe
they mustn't observe 	I mustn't be observing
you mustn't be observing
he mustn't be observing
we mustn't be observing
you mustn't be observing
they mustn't be observing	I mustn't have observed
you mustn't have observed
he mustn't have observed
we mustn't have observed
you mustn't have observed
they mustn't have observed	I mustn't have been observing
you mustn't have been observing
he mustn't have been observing
we mustn't have been observing
you mustn't have been observing
they mustn't have been observing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I observe?
must you observe?
must he observe?
must we observe?
must you observe?
must they observe? 	must I be observing?
must you be observing?
must he be observing?
must we be observing?
must you be observing?
must they be observing? 	must I have observed?
must you have observed?
must he have observed?
must we have observed?
must you have observed?
must they have observed? 	must I have been observing?
must you have been observing?
must he have been observing?
must we have been observing?
must you have been observing?
must they have been observing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I observe?
mustn't you observe?
mustn't he observe?
mustn't we observe?
mustn't you observe?
mustn't they observe? 	mustn't I be observing?
mustn't you be observing?
mustn't he be observing?
mustn't we be observing?
mustn't you be observing?
mustn't they be observing? 	mustn't I have observed?
mustn't you have observed?
mustn't he have observed?
mustn't we have observed?
mustn't you have observed?
mustn't they have observed? 	mustn't I have been observing?
mustn't you have been observing?
mustn't he have been observing?
mustn't we have been observing?
mustn't you have been observing?
mustn't they have been observing?