must decay
Regular verb: decay - decayed- decayed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must decay
you must decay
she must decay
we must decay
you must decay
they must decay 	I must be decaying
you must be decaying
she must be decaying
we must be decaying
you must be decaying
they must be decaying	I must have decayed
you must have decayed
she must have decayed
we must have decayed
you must have decayed
they must have decayed	I must have been decaying
you must have been decaying
she must have been decaying
we must have been decaying
you must have been decaying
they must have been decaying	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't decay
you mustn't decay
she mustn't decay
we mustn't decay
you mustn't decay
they mustn't decay 	I mustn't be decaying
you mustn't be decaying
she mustn't be decaying
we mustn't be decaying
you mustn't be decaying
they mustn't be decaying	I mustn't have decayed
you mustn't have decayed
she mustn't have decayed
we mustn't have decayed
you mustn't have decayed
they mustn't have decayed	I mustn't have been decaying
you mustn't have been decaying
she mustn't have been decaying
we mustn't have been decaying
you mustn't have been decaying
they mustn't have been decaying	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I decay?
must you decay?
must she decay?
must we decay?
must you decay?
must they decay? 	must I be decaying?
must you be decaying?
must she be decaying?
must we be decaying?
must you be decaying?
must they be decaying? 	must I have decayed?
must you have decayed?
must she have decayed?
must we have decayed?
must you have decayed?
must they have decayed? 	must I have been decaying?
must you have been decaying?
must she have been decaying?
must we have been decaying?
must you have been decaying?
must they have been decaying? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I decay?
mustn't you decay?
mustn't she decay?
mustn't we decay?
mustn't you decay?
mustn't they decay? 	mustn't I be decaying?
mustn't you be decaying?
mustn't she be decaying?
mustn't we be decaying?
mustn't you be decaying?
mustn't they be decaying? 	mustn't I have decayed?
mustn't you have decayed?
mustn't she have decayed?
mustn't we have decayed?
mustn't you have decayed?
mustn't they have decayed? 	mustn't I have been decaying?
mustn't you have been decaying?
mustn't she have been decaying?
mustn't we have been decaying?
mustn't you have been decaying?
mustn't they have been decaying?