English verb conjugation
SHOULD STIFFEN

Regular verb: stiffen - stiffened - stiffened

Affirmation

Simple form	V-ing form
I'd stiffen you'd stiffen he'd stiffen we'd stiffen you'd stiffen they'd stiffen	I'd be stiffening you'd be stiffening he'd be stiffening we'd be stiffening you'd be stiffening they'd be stiffening
Perfect	V-ing perfect
I should've stiffened you should've stiffened he should've stiffened we should've stiffened you should've stiffened they should've stiffened	I should've been stiffening you should've been stiffening he should've been stiffening we should've been stiffening you should've been stiffening they should've been stiffening

Negation

Simple form	V-ing form
I shouldn't stiffen you shouldn't stiffen he shouldn't stiffen we shouldn't stiffen you shouldn't stiffen they shouldn't stiffen	I shouldn't be stiffening you shouldn't be stiffening he shouldn't be stiffening we shouldn't be stiffening you shouldn't be stiffening they shouldn't be stiffening
Perfect	V-ing perfect
I shouldn't have stiffened you shouldn't have stiffened he shouldn't have stiffened we shouldn't have stiffened you shouldn't have stiffened they shouldn't have stiffened	I shouldn't have been stiffening you shouldn't have been stiffening he shouldn't have been stiffening we shouldn't have been stiffening you shouldn't have been stiffening they shouldn't have been stiffening

Interrogative form

Simple form	V-ing form
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?
Perfect	V-ing perfect
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
shouldn't I stiffen? shouldn't you stiffen? shouldn't he stiffen? shouldn't we stiffen? shouldn't you stiffen? shouldn't they stiffen?	shouldn't I be stiffening? shouldn't you be stiffening? shouldn't he be stiffening? shouldn't we be stiffening? shouldn't you be stiffening? shouldn't they be stiffening?
Perfect	V-ing perfect
shouldn't I have stiffened? shouldn't you have stiffened? shouldn't he have stiffened? shouldn't we have stiffened? shouldn't you have stiffened? shouldn't they have stiffened?	shouldn't I have been stiffening? shouldn't you have been stiffening? shouldn't he have been stiffening? shouldn't we have been stiffening? shouldn't you have been stiffening? shouldn't they have been stiffening?