could witness
Regular verb: witness - witnessed- witnessed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could witness
you could witness
he could witness
we could witness
you could witness
they could witness 	I could be witnessing
you could be witnessing
he could be witnessing
we could be witnessing
you could be witnessing
they could be witnessing	I could have witnessed
you could have witnessed
he could have witnessed
we could have witnessed
you could have witnessed
they could have witnessed	I could have been witnessing
you could have been witnessing
he could have been witnessing
we could have been witnessing
you could have been witnessing
they could have been witnessing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not witness
you could not witness
he could not witness
we could not witness
you could not witness
they could not witness 	I could not be witnessing
you could not be witnessing
he could not be witnessing
we could not be witnessing
you could not be witnessing
they could not be witnessing	I could not have witnessed
you could not have witnessed
he could not have witnessed
we could not have witnessed
you could not have witnessed
they could not have witnessed	I could not have been witnessing
you could not have been witnessing
he could not have been witnessing
we could not have been witnessing
you could not have been witnessing
they could not have been witnessing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I witness?
could you witness?
could he witness?
could we witness?
could you witness?
could they witness? 	could I be witnessing?
could you be witnessing?
could he be witnessing?
could we be witnessing?
could you be witnessing?
could they be witnessing? 	could I have witnessed?
could you have witnessed?
could he have witnessed?
could we have witnessed?
could you have witnessed?
could they have witnessed? 	could I have been witnessing?
could you have been witnessing?
could he have been witnessing?
could we have been witnessing?
could you have been witnessing?
could they have been witnessing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not witness?
could you not witness?
could he not witness?
could we not witness?
could you not witness?
could they not witness? 	could I not be witnessing?
could you not be witnessing?
could he not be witnessing?
could we not be witnessing?
could you not be witnessing?
could they not be witnessing? 	could I not have witnessed?
could you not have witnessed?
could he not have witnessed?
could we not have witnessed?
could you not have witnessed?
could they not have witnessed? 	could I not have been witnessing?
could you not have been witnessing?
could he not have been witnessing?
could we not have been witnessing?
could you not have been witnessing?
could they not have been witnessing?