could nibble
Regular verb: nibble - nibbled- nibbled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could nibble
you could nibble
she could nibble
we could nibble
you could nibble
they could nibble 	I could be nibbling
you could be nibbling
she could be nibbling
we could be nibbling
you could be nibbling
they could be nibbling	I could have nibbled
you could have nibbled
she could have nibbled
we could have nibbled
you could have nibbled
they could have nibbled	I could have been nibbling
you could have been nibbling
she could have been nibbling
we could have been nibbling
you could have been nibbling
they could have been nibbling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not nibble
you could not nibble
she could not nibble
we could not nibble
you could not nibble
they could not nibble 	I could not be nibbling
you could not be nibbling
she could not be nibbling
we could not be nibbling
you could not be nibbling
they could not be nibbling	I could not have nibbled
you could not have nibbled
she could not have nibbled
we could not have nibbled
you could not have nibbled
they could not have nibbled	I could not have been nibbling
you could not have been nibbling
she could not have been nibbling
we could not have been nibbling
you could not have been nibbling
they could not have been nibbling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I nibble?
could you nibble?
could she nibble?
could we nibble?
could you nibble?
could they nibble? 	could I be nibbling?
could you be nibbling?
could she be nibbling?
could we be nibbling?
could you be nibbling?
could they be nibbling? 	could I have nibbled?
could you have nibbled?
could she have nibbled?
could we have nibbled?
could you have nibbled?
could they have nibbled? 	could I have been nibbling?
could you have been nibbling?
could she have been nibbling?
could we have been nibbling?
could you have been nibbling?
could they have been nibbling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not nibble?
could you not nibble?
could she not nibble?
could we not nibble?
could you not nibble?
could they not nibble? 	could I not be nibbling?
could you not be nibbling?
could she not be nibbling?
could we not be nibbling?
could you not be nibbling?
could they not be nibbling? 	could I not have nibbled?
could you not have nibbled?
could she not have nibbled?
could we not have nibbled?
could you not have nibbled?
could they not have nibbled? 	could I not have been nibbling?
could you not have been nibbling?
could she not have been nibbling?
could we not have been nibbling?
could you not have been nibbling?
could they not have been nibbling?