must yawn
Regular verb: yawn - yawned- yawned

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

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

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

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