must buckle
Regular verb: buckle - buckled- buckled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must buckle
you must buckle
he must buckle
we must buckle
you must buckle
they must buckle 	I must be buckling
you must be buckling
he must be buckling
we must be buckling
you must be buckling
they must be buckling	I must have buckled
you must have buckled
he must have buckled
we must have buckled
you must have buckled
they must have buckled	I must have been buckling
you must have been buckling
he must have been buckling
we must have been buckling
you must have been buckling
they must have been buckling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't buckle
you mustn't buckle
he mustn't buckle
we mustn't buckle
you mustn't buckle
they mustn't buckle 	I mustn't be buckling
you mustn't be buckling
he mustn't be buckling
we mustn't be buckling
you mustn't be buckling
they mustn't be buckling	I mustn't have buckled
you mustn't have buckled
he mustn't have buckled
we mustn't have buckled
you mustn't have buckled
they mustn't have buckled	I mustn't have been buckling
you mustn't have been buckling
he mustn't have been buckling
we mustn't have been buckling
you mustn't have been buckling
they mustn't have been buckling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I buckle?
must you buckle?
must he buckle?
must we buckle?
must you buckle?
must they buckle? 	must I be buckling?
must you be buckling?
must he be buckling?
must we be buckling?
must you be buckling?
must they be buckling? 	must I have buckled?
must you have buckled?
must he have buckled?
must we have buckled?
must you have buckled?
must they have buckled? 	must I have been buckling?
must you have been buckling?
must he have been buckling?
must we have been buckling?
must you have been buckling?
must they have been buckling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I buckle?
mustn't you buckle?
mustn't he buckle?
mustn't we buckle?
mustn't you buckle?
mustn't they buckle? 	mustn't I be buckling?
mustn't you be buckling?
mustn't he be buckling?
mustn't we be buckling?
mustn't you be buckling?
mustn't they be buckling? 	mustn't I have buckled?
mustn't you have buckled?
mustn't he have buckled?
mustn't we have buckled?
mustn't you have buckled?
mustn't they have buckled? 	mustn't I have been buckling?
mustn't you have been buckling?
mustn't he have been buckling?
mustn't we have been buckling?
mustn't you have been buckling?
mustn't they have been buckling?