I must founder you must founder she must founder we must founder you must founder they must founder
V-ing form
I must be foundering you must be foundering she must be foundering we must be foundering you must be foundering they must be foundering
Perfect
I must have foundered you must have foundered she must have foundered we must have foundered you must have foundered they must have foundered
V-ing perfect
I must have been foundering you must have been foundering she must have been foundering we must have been foundering you must have been foundering they must have been foundering
Negation
Simple form
I mustn't founder you mustn't founder she mustn't founder we mustn't founder you mustn't founder they mustn't founder
V-ing form
I mustn't be foundering you mustn't be foundering she mustn't be foundering we mustn't be foundering you mustn't be foundering they mustn't be foundering
Perfect
I mustn't have foundered you mustn't have foundered she mustn't have foundered we mustn't have foundered you mustn't have foundered they mustn't have foundered
V-ing perfect
I mustn't have been foundering you mustn't have been foundering she mustn't have been foundering we mustn't have been foundering you mustn't have been foundering they mustn't have been foundering
Interrogative form
Simple form
must I founder? must you founder? must she founder? must we founder? must you founder? must they founder?
V-ing form
must I be foundering? must you be foundering? must she be foundering? must we be foundering? must you be foundering? must they be foundering?
Perfect
must I have foundered? must you have foundered? must she have foundered? must we have foundered? must you have foundered? must they have foundered?
V-ing perfect
must I have been foundering? must you have been foundering? must she have been foundering? must we have been foundering? must you have been foundering? must they have been foundering?
Interro-negative form
Simple form
mustn't I founder? mustn't you founder? mustn't she founder? mustn't we founder? mustn't you founder? mustn't they founder?
V-ing form
mustn't I be foundering? mustn't you be foundering? mustn't she be foundering? mustn't we be foundering? mustn't you be foundering? mustn't they be foundering?
Perfect
mustn't I have foundered? mustn't you have foundered? mustn't she have foundered? mustn't we have foundered? mustn't you have foundered? mustn't they have foundered?
V-ing perfect
mustn't I have been foundering? mustn't you have been foundering? mustn't she have been foundering? mustn't we have been foundering? mustn't you have been foundering? mustn't they have been foundering?