could knuckle
Regular verb: knuckle - knuckled- knuckled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could knuckle
you could knuckle
he could knuckle
we could knuckle
you could knuckle
they could knuckle 	I could be knuckling
you could be knuckling
he could be knuckling
we could be knuckling
you could be knuckling
they could be knuckling	I could have knuckled
you could have knuckled
he could have knuckled
we could have knuckled
you could have knuckled
they could have knuckled	I could have been knuckling
you could have been knuckling
he could have been knuckling
we could have been knuckling
you could have been knuckling
they could have been knuckling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't knuckle
you couldn't knuckle
he couldn't knuckle
we couldn't knuckle
you couldn't knuckle
they couldn't knuckle 	I couldn't be knuckling
you couldn't be knuckling
he couldn't be knuckling
we couldn't be knuckling
you couldn't be knuckling
they couldn't be knuckling	I couldn't have knuckled
you couldn't have knuckled
he couldn't have knuckled
we couldn't have knuckled
you couldn't have knuckled
they couldn't have knuckled	I couldn't have been knuckling
you couldn't have been knuckling
he couldn't have been knuckling
we couldn't have been knuckling
you couldn't have been knuckling
they couldn't have been knuckling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I knuckle?
could you knuckle?
could he knuckle?
could we knuckle?
could you knuckle?
could they knuckle? 	could I be knuckling?
could you be knuckling?
could he be knuckling?
could we be knuckling?
could you be knuckling?
could they be knuckling? 	could I have knuckled?
could you have knuckled?
could he have knuckled?
could we have knuckled?
could you have knuckled?
could they have knuckled? 	could I have been knuckling?
could you have been knuckling?
could he have been knuckling?
could we have been knuckling?
could you have been knuckling?
could they have been knuckling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I knuckle?
couldn't you knuckle?
couldn't he knuckle?
couldn't we knuckle?
couldn't you knuckle?
couldn't they knuckle? 	couldn't I be knuckling?
couldn't you be knuckling?
couldn't he be knuckling?
couldn't we be knuckling?
couldn't you be knuckling?
couldn't they be knuckling? 	couldn't I have knuckled?
couldn't you have knuckled?
couldn't he have knuckled?
couldn't we have knuckled?
couldn't you have knuckled?
couldn't they have knuckled? 	couldn't I have been knuckling?
couldn't you have been knuckling?
couldn't he have been knuckling?
couldn't we have been knuckling?
couldn't you have been knuckling?
couldn't they have been knuckling?