English verb conjugation
COULD STIFF

Regular verb: stiff - stiffed - stiffed

Affirmation

Simple form	V-ing form
I could stiff you could stiff he could stiff we could stiff you could stiff they could stiff	I could be stiffing you could be stiffing he could be stiffing we could be stiffing you could be stiffing they could be stiffing
Perfect	V-ing perfect
I could have stiffed you could have stiffed he could have stiffed we could have stiffed you could have stiffed they could have stiffed	I could have been stiffing you could have been stiffing he could have been stiffing we could have been stiffing you could have been stiffing they could have been stiffing

Negation

Simple form	V-ing form
I could not stiff you could not stiff he could not stiff we could not stiff you could not stiff they could not stiff	I could not be stiffing you could not be stiffing he could not be stiffing we could not be stiffing you could not be stiffing they could not be stiffing
Perfect	V-ing perfect
I could not have stiffed you could not have stiffed he could not have stiffed we could not have stiffed you could not have stiffed they could not have stiffed	I could not have been stiffing you could not have been stiffing he could not have been stiffing we could not have been stiffing you could not have been stiffing they could not have been stiffing

Interrogative form

Simple form	V-ing form
could I stiff? could you stiff? could he stiff? could we stiff? could you stiff? could they stiff?	could I be stiffing? could you be stiffing? could he be stiffing? could we be stiffing? could you be stiffing? could they be stiffing?
Perfect	V-ing perfect
could I have stiffed? could you have stiffed? could he have stiffed? could we have stiffed? could you have stiffed? could they have stiffed?	could I have been stiffing? could you have been stiffing? could he have been stiffing? could we have been stiffing? could you have been stiffing? could they have been stiffing?

Interro-negative form

Simple form	V-ing form
could I not stiff? could you not stiff? could he not stiff? could we not stiff? could you not stiff? could they not stiff?	could I not be stiffing? could you not be stiffing? could he not be stiffing? could we not be stiffing? could you not be stiffing? could they not be stiffing?
Perfect	V-ing perfect
could I not have stiffed? could you not have stiffed? could he not have stiffed? could we not have stiffed? could you not have stiffed? could they not have stiffed?	could I not have been stiffing? could you not have been stiffing? could he not have been stiffing? could we not have been stiffing? could you not have been stiffing? could they not have been stiffing?