could yak
Regular verb: yak - yaked- yaked

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could yak
you could yak
he could yak
we could yak
you could yak
they could yak 	I could be yaking
you could be yaking
he could be yaking
we could be yaking
you could be yaking
they could be yaking	I could have yaked
you could have yaked
he could have yaked
we could have yaked
you could have yaked
they could have yaked	I could have been yaking
you could have been yaking
he could have been yaking
we could have been yaking
you could have been yaking
they could have been yaking	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't yak
you couldn't yak
he couldn't yak
we couldn't yak
you couldn't yak
they couldn't yak 	I couldn't be yaking
you couldn't be yaking
he couldn't be yaking
we couldn't be yaking
you couldn't be yaking
they couldn't be yaking	I couldn't have yaked
you couldn't have yaked
he couldn't have yaked
we couldn't have yaked
you couldn't have yaked
they couldn't have yaked	I couldn't have been yaking
you couldn't have been yaking
he couldn't have been yaking
we couldn't have been yaking
you couldn't have been yaking
they couldn't have been yaking	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I yak?
could you yak?
could he yak?
could we yak?
could you yak?
could they yak? 	could I be yaking?
could you be yaking?
could he be yaking?
could we be yaking?
could you be yaking?
could they be yaking? 	could I have yaked?
could you have yaked?
could he have yaked?
could we have yaked?
could you have yaked?
could they have yaked? 	could I have been yaking?
could you have been yaking?
could he have been yaking?
could we have been yaking?
could you have been yaking?
could they have been yaking? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I yak?
couldn't you yak?
couldn't he yak?
couldn't we yak?
couldn't you yak?
couldn't they yak? 	couldn't I be yaking?
couldn't you be yaking?
couldn't he be yaking?
couldn't we be yaking?
couldn't you be yaking?
couldn't they be yaking? 	couldn't I have yaked?
couldn't you have yaked?
couldn't he have yaked?
couldn't we have yaked?
couldn't you have yaked?
couldn't they have yaked? 	couldn't I have been yaking?
couldn't you have been yaking?
couldn't he have been yaking?
couldn't we have been yaking?
couldn't you have been yaking?
couldn't they have been yaking?