must toughen
Regular verb: toughen - toughened- toughened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must toughen
you must toughen
she must toughen
we must toughen
you must toughen
they must toughen 	I must be toughening
you must be toughening
she must be toughening
we must be toughening
you must be toughening
they must be toughening	I must have toughened
you must have toughened
she must have toughened
we must have toughened
you must have toughened
they must have toughened	I must have been toughening
you must have been toughening
she must have been toughening
we must have been toughening
you must have been toughening
they must have been toughening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must not toughen
you must not toughen
she must not toughen
we must not toughen
you must not toughen
they must not toughen 	I must not be toughening
you must not be toughening
she must not be toughening
we must not be toughening
you must not be toughening
they must not be toughening	I must not have toughened
you must not have toughened
she must not have toughened
we must not have toughened
you must not have toughened
they must not have toughened	I must not have been toughening
you must not have been toughening
she must not have been toughening
we must not have been toughening
you must not have been toughening
they must not have been toughening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I toughen?
must you toughen?
must she toughen?
must we toughen?
must you toughen?
must they toughen? 	must I be toughening?
must you be toughening?
must she be toughening?
must we be toughening?
must you be toughening?
must they be toughening? 	must I have toughened?
must you have toughened?
must she have toughened?
must we have toughened?
must you have toughened?
must they have toughened? 	must I have been toughening?
must you have been toughening?
must she have been toughening?
must we have been toughening?
must you have been toughening?
must they have been toughening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I not toughen?
must you not toughen?
must she not toughen?
must we not toughen?
must you not toughen?
must they not toughen? 	must I not be toughening?
must you not be toughening?
must she not be toughening?
must we not be toughening?
must you not be toughening?
must they not be toughening? 	must I not have toughened?
must you not have toughened?
must she not have toughened?
must we not have toughened?
must you not have toughened?
must they not have toughened? 	must I not have been toughening?
must you not have been toughening?
must she not have been toughening?
must we not have been toughening?
must you not have been toughening?
must they not have been toughening?