could stiff
Regular verb: stiff - stiffed- stiffed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could stiff
you could stiff
she could stiff
we could stiff
you could stiff
they could stiff 	I could be stiffing
you could be stiffing
she could be stiffing
we could be stiffing
you could be stiffing
they could be stiffing	I could have stiffed
you could have stiffed
she 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
she 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 	Perfect 	V-ing perfect 	
I couldn't stiff
you couldn't stiff
she couldn't stiff
we couldn't stiff
you couldn't stiff
they couldn't stiff 	I couldn't be stiffing
you couldn't be stiffing
she couldn't be stiffing
we couldn't be stiffing
you couldn't be stiffing
they couldn't be stiffing	I couldn't have stiffed
you couldn't have stiffed
she couldn't have stiffed
we couldn't have stiffed
you couldn't have stiffed
they couldn't have stiffed	I couldn't have been stiffing
you couldn't have been stiffing
she couldn't have been stiffing
we couldn't have been stiffing
you couldn't have been stiffing
they couldn't have been stiffing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I stiff?
could you stiff?
could she stiff?
could we stiff?
could you stiff?
could they stiff? 	could I be stiffing?
could you be stiffing?
could she be stiffing?
could we be stiffing?
could you be stiffing?
could they be stiffing? 	could I have stiffed?
could you have stiffed?
could she 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 she 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 	Perfect 	V-ing perfect 	
couldn't I stiff?
couldn't you stiff?
couldn't she stiff?
couldn't we stiff?
couldn't you stiff?
couldn't they stiff? 	couldn't I be stiffing?
couldn't you be stiffing?
couldn't she be stiffing?
couldn't we be stiffing?
couldn't you be stiffing?
couldn't they be stiffing? 	couldn't I have stiffed?
couldn't you have stiffed?
couldn't she have stiffed?
couldn't we have stiffed?
couldn't you have stiffed?
couldn't they have stiffed? 	couldn't I have been stiffing?
couldn't you have been stiffing?
couldn't she have been stiffing?
couldn't we have been stiffing?
couldn't you have been stiffing?
couldn't they have been stiffing?