English verb conjugation
SHOULD STIFFEN

Regular verb: stiffen - stiffened - stiffened

Affirmation

Simple form	V-ing form
I'd stiffen you'd stiffen she'd stiffen we'd stiffen you'd stiffen they'd stiffen	I'd be stiffening you'd be stiffening she'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 she 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 she 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 she 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 she 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 she 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 she 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 she stiffen? should we stiffen? should you stiffen? should they stiffen?	should I be stiffening? should you be stiffening? should she 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 she 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 she 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 she 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 she 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 she 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 she have been stiffening? shouldn't we have been stiffening? shouldn't you have been stiffening? shouldn't they have been stiffening?