should stiffen
Regular verb: stiffen - stiffened- stiffened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I should stiffen
you should stiffen
he should stiffen
we should stiffen
you should stiffen
they should stiffen 	I should be stiffening
you should be stiffening
he should be stiffening
we should be stiffening
you should be stiffening
they should be stiffening	I should have stiffened
you should have stiffened
he should have stiffened
we should have stiffened
you should have stiffened
they should have stiffened	I should have been stiffening
you should have been stiffening
he should have been stiffening
we should have been stiffening
you should have been stiffening
they should have been stiffening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I should not stiffen
you should not stiffen
he should not stiffen
we should not stiffen
you should not stiffen
they should not stiffen 	I should not be stiffening
you should not be stiffening
he should not be stiffening
we should not be stiffening
you should not be stiffening
they should not be stiffening	I should not have stiffened
you should not have stiffened
he should not have stiffened
we should not have stiffened
you should not have stiffened
they should not have stiffened	I should not have been stiffening
you should not have been stiffening
he should not have been stiffening
we should not have been stiffening
you should not have been stiffening
they should not have been stiffening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
should I stiffen?
should you stiffen?
should he stiffen?
should we stiffen?
should you stiffen?
should they stiffen? 	should I be stiffening?
should you be stiffening?
should he be stiffening?
should we be stiffening?
should you be stiffening?
should they be stiffening? 	should I have stiffened?
should you have stiffened?
should he have stiffened?
should we have stiffened?
should you have stiffened?
should they have stiffened? 	should I have been stiffening?
should you have been stiffening?
should he have been stiffening?
should we have been stiffening?
should you have been stiffening?
should they have been stiffening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
should I not stiffen?
should you not stiffen?
should he not stiffen?
should we not stiffen?
should you not stiffen?
should they not stiffen? 	should I not be stiffening?
should you not be stiffening?
should he not be stiffening?
should we not be stiffening?
should you not be stiffening?
should they not be stiffening? 	should I not have stiffened?
should you not have stiffened?
should he not have stiffened?
should we not have stiffened?
should you not have stiffened?
should they not have stiffened? 	should I not have been stiffening?
should you not have been stiffening?
should he not have been stiffening?
should we not have been stiffening?
should you not have been stiffening?
should they not have been stiffening?