could riff
Regular verb: riff - riffed- riffed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could riff
you could riff
she could riff
we could riff
you could riff
they could riff 	I could be riffing
you could be riffing
she could be riffing
we could be riffing
you could be riffing
they could be riffing	I could have riffed
you could have riffed
she could have riffed
we could have riffed
you could have riffed
they could have riffed	I could have been riffing
you could have been riffing
she could have been riffing
we could have been riffing
you could have been riffing
they could have been riffing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not riff
you could not riff
she could not riff
we could not riff
you could not riff
they could not riff 	I could not be riffing
you could not be riffing
she could not be riffing
we could not be riffing
you could not be riffing
they could not be riffing	I could not have riffed
you could not have riffed
she could not have riffed
we could not have riffed
you could not have riffed
they could not have riffed	I could not have been riffing
you could not have been riffing
she could not have been riffing
we could not have been riffing
you could not have been riffing
they could not have been riffing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I riff?
could you riff?
could she riff?
could we riff?
could you riff?
could they riff? 	could I be riffing?
could you be riffing?
could she be riffing?
could we be riffing?
could you be riffing?
could they be riffing? 	could I have riffed?
could you have riffed?
could she have riffed?
could we have riffed?
could you have riffed?
could they have riffed? 	could I have been riffing?
could you have been riffing?
could she have been riffing?
could we have been riffing?
could you have been riffing?
could they have been riffing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not riff?
could you not riff?
could she not riff?
could we not riff?
could you not riff?
could they not riff? 	could I not be riffing?
could you not be riffing?
could she not be riffing?
could we not be riffing?
could you not be riffing?
could they not be riffing? 	could I not have riffed?
could you not have riffed?
could she not have riffed?
could we not have riffed?
could you not have riffed?
could they not have riffed? 	could I not have been riffing?
could you not have been riffing?
could she not have been riffing?
could we not have been riffing?
could you not have been riffing?
could they not have been riffing?