could null
Regular verb: null - nulled- nulled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could null
you could null
he could null
we could null
you could null
they could null 	I could be nulling
you could be nulling
he could be nulling
we could be nulling
you could be nulling
they could be nulling	I could have nulled
you could have nulled
he could have nulled
we could have nulled
you could have nulled
they could have nulled	I could have been nulling
you could have been nulling
he could have been nulling
we could have been nulling
you could have been nulling
they could have been nulling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't null
you couldn't null
he couldn't null
we couldn't null
you couldn't null
they couldn't null 	I couldn't be nulling
you couldn't be nulling
he couldn't be nulling
we couldn't be nulling
you couldn't be nulling
they couldn't be nulling	I couldn't have nulled
you couldn't have nulled
he couldn't have nulled
we couldn't have nulled
you couldn't have nulled
they couldn't have nulled	I couldn't have been nulling
you couldn't have been nulling
he couldn't have been nulling
we couldn't have been nulling
you couldn't have been nulling
they couldn't have been nulling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I null?
could you null?
could he null?
could we null?
could you null?
could they null? 	could I be nulling?
could you be nulling?
could he be nulling?
could we be nulling?
could you be nulling?
could they be nulling? 	could I have nulled?
could you have nulled?
could he have nulled?
could we have nulled?
could you have nulled?
could they have nulled? 	could I have been nulling?
could you have been nulling?
could he have been nulling?
could we have been nulling?
could you have been nulling?
could they have been nulling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I null?
couldn't you null?
couldn't he null?
couldn't we null?
couldn't you null?
couldn't they null? 	couldn't I be nulling?
couldn't you be nulling?
couldn't he be nulling?
couldn't we be nulling?
couldn't you be nulling?
couldn't they be nulling? 	couldn't I have nulled?
couldn't you have nulled?
couldn't he have nulled?
couldn't we have nulled?
couldn't you have nulled?
couldn't they have nulled? 	couldn't I have been nulling?
couldn't you have been nulling?
couldn't he have been nulling?
couldn't we have been nulling?
couldn't you have been nulling?
couldn't they have been nulling?