could filter
Regular verb: filter - filtered- filtered

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could filter
you could filter
she could filter
we could filter
you could filter
they could filter 	I could be filtering
you could be filtering
she could be filtering
we could be filtering
you could be filtering
they could be filtering	I could have filtered
you could have filtered
she could have filtered
we could have filtered
you could have filtered
they could have filtered	I could have been filtering
you could have been filtering
she could have been filtering
we could have been filtering
you could have been filtering
they could have been filtering	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't filter
you couldn't filter
she couldn't filter
we couldn't filter
you couldn't filter
they couldn't filter 	I couldn't be filtering
you couldn't be filtering
she couldn't be filtering
we couldn't be filtering
you couldn't be filtering
they couldn't be filtering	I couldn't have filtered
you couldn't have filtered
she couldn't have filtered
we couldn't have filtered
you couldn't have filtered
they couldn't have filtered	I couldn't have been filtering
you couldn't have been filtering
she couldn't have been filtering
we couldn't have been filtering
you couldn't have been filtering
they couldn't have been filtering	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I filter?
could you filter?
could she filter?
could we filter?
could you filter?
could they filter? 	could I be filtering?
could you be filtering?
could she be filtering?
could we be filtering?
could you be filtering?
could they be filtering? 	could I have filtered?
could you have filtered?
could she have filtered?
could we have filtered?
could you have filtered?
could they have filtered? 	could I have been filtering?
could you have been filtering?
could she have been filtering?
could we have been filtering?
could you have been filtering?
could they have been filtering? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I filter?
couldn't you filter?
couldn't she filter?
couldn't we filter?
couldn't you filter?
couldn't they filter? 	couldn't I be filtering?
couldn't you be filtering?
couldn't she be filtering?
couldn't we be filtering?
couldn't you be filtering?
couldn't they be filtering? 	couldn't I have filtered?
couldn't you have filtered?
couldn't she have filtered?
couldn't we have filtered?
couldn't you have filtered?
couldn't they have filtered? 	couldn't I have been filtering?
couldn't you have been filtering?
couldn't she have been filtering?
couldn't we have been filtering?
couldn't you have been filtering?
couldn't they have been filtering?