could yawn
Regular verb: yawn - yawned- yawned

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could yawn
you could yawn
he could yawn
we could yawn
you could yawn
they could yawn 	I could be yawning
you could be yawning
he could be yawning
we could be yawning
you could be yawning
they could be yawning	I could have yawned
you could have yawned
he could have yawned
we could have yawned
you could have yawned
they could have yawned	I could have been yawning
you could have been yawning
he could have been yawning
we could have been yawning
you could have been yawning
they could have been yawning	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't yawn
you couldn't yawn
he couldn't yawn
we couldn't yawn
you couldn't yawn
they couldn't yawn 	I couldn't be yawning
you couldn't be yawning
he couldn't be yawning
we couldn't be yawning
you couldn't be yawning
they couldn't be yawning	I couldn't have yawned
you couldn't have yawned
he couldn't have yawned
we couldn't have yawned
you couldn't have yawned
they couldn't have yawned	I couldn't have been yawning
you couldn't have been yawning
he couldn't have been yawning
we couldn't have been yawning
you couldn't have been yawning
they couldn't have been yawning	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I yawn?
could you yawn?
could he yawn?
could we yawn?
could you yawn?
could they yawn? 	could I be yawning?
could you be yawning?
could he be yawning?
could we be yawning?
could you be yawning?
could they be yawning? 	could I have yawned?
could you have yawned?
could he have yawned?
could we have yawned?
could you have yawned?
could they have yawned? 	could I have been yawning?
could you have been yawning?
could he have been yawning?
could we have been yawning?
could you have been yawning?
could they have been yawning? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I yawn?
couldn't you yawn?
couldn't he yawn?
couldn't we yawn?
couldn't you yawn?
couldn't they yawn? 	couldn't I be yawning?
couldn't you be yawning?
couldn't he be yawning?
couldn't we be yawning?
couldn't you be yawning?
couldn't they be yawning? 	couldn't I have yawned?
couldn't you have yawned?
couldn't he have yawned?
couldn't we have yawned?
couldn't you have yawned?
couldn't they have yawned? 	couldn't I have been yawning?
couldn't you have been yawning?
couldn't he have been yawning?
couldn't we have been yawning?
couldn't you have been yawning?
couldn't they have been yawning?