could yawn
Regular verb: yawn - yawned- yawned

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could yawn
you could yawn
she could yawn
we could yawn
you could yawn
they could yawn 	I could be yawning
you could be yawning
she could be yawning
we could be yawning
you could be yawning
they could be yawning	I could have yawned
you could have yawned
she 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
she 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
she 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
she 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
she 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
she 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 she yawn?
could we yawn?
could you yawn?
could they yawn? 	could I be yawning?
could you be yawning?
could she be yawning?
could we be yawning?
could you be yawning?
could they be yawning? 	could I have yawned?
could you have yawned?
could she 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 she 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 she 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 she 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 she 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 she have been yawning?
couldn't we have been yawning?
couldn't you have been yawning?
couldn't they have been yawning?