I must birl you must birl he must birl we must birl you must birl they must birl
V-ing form
I must be birling you must be birling he must be birling we must be birling you must be birling they must be birling
Perfect
I must have birled you must have birled he must have birled we must have birled you must have birled they must have birled
V-ing perfect
I must have been birling you must have been birling he must have been birling we must have been birling you must have been birling they must have been birling
Negation
Simple form
I mustn't birl you mustn't birl he mustn't birl we mustn't birl you mustn't birl they mustn't birl
V-ing form
I mustn't be birling you mustn't be birling he mustn't be birling we mustn't be birling you mustn't be birling they mustn't be birling
Perfect
I mustn't have birled you mustn't have birled he mustn't have birled we mustn't have birled you mustn't have birled they mustn't have birled
V-ing perfect
I mustn't have been birling you mustn't have been birling he mustn't have been birling we mustn't have been birling you mustn't have been birling they mustn't have been birling
Interrogative form
Simple form
must I birl? must you birl? must he birl? must we birl? must you birl? must they birl?
V-ing form
must I be birling? must you be birling? must he be birling? must we be birling? must you be birling? must they be birling?
Perfect
must I have birled? must you have birled? must he have birled? must we have birled? must you have birled? must they have birled?
V-ing perfect
must I have been birling? must you have been birling? must he have been birling? must we have been birling? must you have been birling? must they have been birling?
Interro-negative form
Simple form
mustn't I birl? mustn't you birl? mustn't he birl? mustn't we birl? mustn't you birl? mustn't they birl?
V-ing form
mustn't I be birling? mustn't you be birling? mustn't he be birling? mustn't we be birling? mustn't you be birling? mustn't they be birling?
Perfect
mustn't I have birled? mustn't you have birled? mustn't he have birled? mustn't we have birled? mustn't you have birled? mustn't they have birled?
V-ing perfect
mustn't I have been birling? mustn't you have been birling? mustn't he have been birling? mustn't we have been birling? mustn't you have been birling? mustn't they have been birling?