I must found you must found he must found we must found you must found they must found
V-ing form
I must be founding you must be founding he must be founding we must be founding you must be founding they must be founding
Perfect
I must have founded you must have founded he 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 he 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 he 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 he 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 he 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 he 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 he found? must we found? must you found? must they found?
V-ing form
must I be founding? must you be founding? must he be founding? must we be founding? must you be founding? must they be founding?
Perfect
must I have founded? must you have founded? must he 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 he 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 he 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 he 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 he 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 he have been founding? mustn't we have been founding? mustn't you have been founding? mustn't they have been founding?