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 must not decay
you must not decay
she must not decay
we must not decay
you must not decay
they must not decay 	I must not be decaying
you must not be decaying
she must not be decaying
we must not be decaying
you must not be decaying
they must not be decaying	I must not have decayed
you must not have decayed
she must not have decayed
we must not have decayed
you must not have decayed
they must not have decayed	I must not have been decaying
you must not have been decaying
she must not have been decaying
we must not have been decaying
you must not have been decaying
they must not 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 	
must I not decay?
must you not decay?
must she not decay?
must we not decay?
must you not decay?
must they not decay? 	must I not be decaying?
must you not be decaying?
must she not be decaying?
must we not be decaying?
must you not be decaying?
must they not be decaying? 	must I not have decayed?
must you not have decayed?
must she not have decayed?
must we not have decayed?
must you not have decayed?
must they not have decayed? 	must I not have been decaying?
must you not have been decaying?
must she not have been decaying?
must we not have been decaying?
must you not have been decaying?
must they not have been decaying?