I can stiffen you can stiffen she can stiffen we can stiffen you can stiffen they can stiffen
V-ing form
I can be stiffening you can be stiffening she can be stiffening we can be stiffening you can be stiffening they can be stiffening
Perfect
I can have stiffened you can have stiffened she can have stiffened we can have stiffened you can have stiffened they can have stiffened
V-ing perfect
I can have been stiffening you can have been stiffening she can have been stiffening we can have been stiffening you can have been stiffening they can have been stiffening
Negation
Simple form
I cannot stiffen you cannot stiffen she cannot stiffen we cannot stiffen you cannot stiffen they cannot stiffen
V-ing form
I cannot be stiffening you cannot be stiffening she cannot be stiffening we cannot be stiffening you cannot be stiffening they cannot be stiffening
Perfect
I cannot have stiffened you cannot have stiffened she cannot have stiffened we cannot have stiffened you cannot have stiffened they cannot have stiffened
V-ing perfect
I cannot have been stiffening you cannot have been stiffening she cannot have been stiffening we cannot have been stiffening you cannot have been stiffening they cannot have been stiffening
Interrogative form
Simple form
can I stiffen? can you stiffen? can she stiffen? can we stiffen? can you stiffen? can they stiffen?
V-ing form
can I be stiffening? can you be stiffening? can she be stiffening? can we be stiffening? can you be stiffening? can they be stiffening?
Perfect
can I have stiffened? can you have stiffened? can she have stiffened? can we have stiffened? can you have stiffened? can they have stiffened?
V-ing perfect
can I have been stiffening? can you have been stiffening? can she have been stiffening? can we have been stiffening? can you have been stiffening? can they have been stiffening?
Interro-negative form
Simple form
can I not stiffen? can you not stiffen? can she not stiffen? can we not stiffen? can you not stiffen? can they not stiffen?
V-ing form
can I not be stiffening? can you not be stiffening? can she not be stiffening? can we not be stiffening? can you not be stiffening? can they not be stiffening?
Perfect
can I not have stiffened? can you not have stiffened? can she not have stiffened? can we not have stiffened? can you not have stiffened? can they not have stiffened?
V-ing perfect
can I not have been stiffening? can you not have been stiffening? can she not have been stiffening? can we not have been stiffening? can you not have been stiffening? can they not have been stiffening?