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 could not yawn
you could not yawn
he could not yawn
we could not yawn
you could not yawn
they could not yawn 	I could not be yawning
you could not be yawning
he could not be yawning
we could not be yawning
you could not be yawning
they could not be yawning	I could not have yawned
you could not have yawned
he could not have yawned
we could not have yawned
you could not have yawned
they could not have yawned	I could not have been yawning
you could not have been yawning
he could not have been yawning
we could not have been yawning
you could not have been yawning
they could not 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 	
could I not yawn?
could you not yawn?
could he not yawn?
could we not yawn?
could you not yawn?
could they not yawn? 	could I not be yawning?
could you not be yawning?
could he not be yawning?
could we not be yawning?
could you not be yawning?
could they not be yawning? 	could I not have yawned?
could you not have yawned?
could he not have yawned?
could we not have yawned?
could you not have yawned?
could they not have yawned? 	could I not have been yawning?
could you not have been yawning?
could he not have been yawning?
could we not have been yawning?
could you not have been yawning?
could they not have been yawning?