must yawn
Regular verb: yawn - yawned- yawned

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