I must birl you must birl she must birl we must birl you must birl they must birl
V-ing form
I must be birling you must be birling she must be birling we must be birling you must be birling they must be birling
Perfect
I must have birled you must have birled she 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 she must have been birling we must have been birling you must have been birling they must have been birling
Negation
Simple form
I must not birl you must not birl she must not birl we must not birl you must not birl they must not birl
V-ing form
I must not be birling you must not be birling she must not be birling we must not be birling you must not be birling they must not be birling
Perfect
I must not have birled you must not have birled she must not have birled we must not have birled you must not have birled they must not have birled
V-ing perfect
I must not have been birling you must not have been birling she must not have been birling we must not have been birling you must not have been birling they must not have been birling
Interrogative form
Simple form
must I birl? must you birl? must she birl? must we birl? must you birl? must they birl?
V-ing form
must I be birling? must you be birling? must she be birling? must we be birling? must you be birling? must they be birling?
Perfect
must I have birled? must you have birled? must she 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 she have been birling? must we have been birling? must you have been birling? must they have been birling?
Interro-negative form
Simple form
must I not birl? must you not birl? must she not birl? must we not birl? must you not birl? must they not birl?
V-ing form
must I not be birling? must you not be birling? must she not be birling? must we not be birling? must you not be birling? must they not be birling?
Perfect
must I not have birled? must you not have birled? must she not have birled? must we not have birled? must you not have birled? must they not have birled?
V-ing perfect
must I not have been birling? must you not have been birling? must she not have been birling? must we not have been birling? must you not have been birling? must they not have been birling?