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