must observe
Verbo regular: observe - observed- observed

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
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	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I must not observe
you must not observe
he must not observe
we must not observe
you must not observe
they must not observe 	I must not be observing
you must not be observing
he must not be observing
we must not be observing
you must not be observing
they must not be observing	I must not have observed
you must not have observed
he must not have observed
we must not have observed
you must not have observed
they must not have observed	I must not have been observing
you must not have been observing
he must not have been observing
we must not have been observing
you must not have been observing
they must not have been observing	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
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? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
must I not observe?
must you not observe?
must he not observe?
must we not observe?
must you not observe?
must they not observe? 	must I not be observing?
must you not be observing?
must he not be observing?
must we not be observing?
must you not be observing?
must they not be observing? 	must I not have observed?
must you not have observed?
must he not have observed?
must we not have observed?
must you not have observed?
must they not have observed? 	must I not have been observing?
must you not have been observing?
must he not have been observing?
must we not have been observing?
must you not have been observing?
must they not have been observing?