must occur
Verbo regular: occur - occurred- occurred

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I must occur
you must occur
he must occur
we must occur
you must occur
they must occur 	I must be occurring
you must be occurring
he must be occurring
we must be occurring
you must be occurring
they must be occurring	I must have occurred
you must have occurred
he must have occurred
we must have occurred
you must have occurred
they must have occurred	I must have been occurring
you must have been occurring
he must have been occurring
we must have been occurring
you must have been occurring
they must have been occurring	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I mustn't occur
you mustn't occur
he mustn't occur
we mustn't occur
you mustn't occur
they mustn't occur 	I mustn't be occurring
you mustn't be occurring
he mustn't be occurring
we mustn't be occurring
you mustn't be occurring
they mustn't be occurring	I mustn't have occurred
you mustn't have occurred
he mustn't have occurred
we mustn't have occurred
you mustn't have occurred
they mustn't have occurred	I mustn't have been occurring
you mustn't have been occurring
he mustn't have been occurring
we mustn't have been occurring
you mustn't have been occurring
they mustn't have been occurring	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
must I occur?
must you occur?
must he occur?
must we occur?
must you occur?
must they occur? 	must I be occurring?
must you be occurring?
must he be occurring?
must we be occurring?
must you be occurring?
must they be occurring? 	must I have occurred?
must you have occurred?
must he have occurred?
must we have occurred?
must you have occurred?
must they have occurred? 	must I have been occurring?
must you have been occurring?
must he have been occurring?
must we have been occurring?
must you have been occurring?
must they have been occurring? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
mustn't I occur?
mustn't you occur?
mustn't he occur?
mustn't we occur?
mustn't you occur?
mustn't they occur? 	mustn't I be occurring?
mustn't you be occurring?
mustn't he be occurring?
mustn't we be occurring?
mustn't you be occurring?
mustn't they be occurring? 	mustn't I have occurred?
mustn't you have occurred?
mustn't he have occurred?
mustn't we have occurred?
mustn't you have occurred?
mustn't they have occurred? 	mustn't I have been occurring?
mustn't you have been occurring?
mustn't he have been occurring?
mustn't we have been occurring?
mustn't you have been occurring?
mustn't they have been occurring?