English verb conjugation
CAN STIFFEN

Regular verb: stiffen - stiffened - stiffened

Affirmation

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

Negation

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

Interrogative form

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

Interro-negative form

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