I must investigate you must investigate she must investigate we must investigate you must investigate they must investigate
V-ing form
I must be investigating you must be investigating she must be investigating we must be investigating you must be investigating they must be investigating
Perfect
I must have investigated you must have investigated she must have investigated we must have investigated you must have investigated they must have investigated
V-ing perfect
I must have been investigating you must have been investigating she must have been investigating we must have been investigating you must have been investigating they must have been investigating
Negation
Simple form
I must not investigate you must not investigate she must not investigate we must not investigate you must not investigate they must not investigate
V-ing form
I must not be investigating you must not be investigating she must not be investigating we must not be investigating you must not be investigating they must not be investigating
Perfect
I must not have investigated you must not have investigated she must not have investigated we must not have investigated you must not have investigated they must not have investigated
V-ing perfect
I must not have been investigating you must not have been investigating she must not have been investigating we must not have been investigating you must not have been investigating they must not have been investigating
Interrogative form
Simple form
must I investigate? must you investigate? must she investigate? must we investigate? must you investigate? must they investigate?
V-ing form
must I be investigating? must you be investigating? must she be investigating? must we be investigating? must you be investigating? must they be investigating?
Perfect
must I have investigated? must you have investigated? must she have investigated? must we have investigated? must you have investigated? must they have investigated?
V-ing perfect
must I have been investigating? must you have been investigating? must she have been investigating? must we have been investigating? must you have been investigating? must they have been investigating?
Interro-negative form
Simple form
must I not investigate? must you not investigate? must she not investigate? must we not investigate? must you not investigate? must they not investigate?
V-ing form
must I not be investigating? must you not be investigating? must she not be investigating? must we not be investigating? must you not be investigating? must they not be investigating?
Perfect
must I not have investigated? must you not have investigated? must she not have investigated? must we not have investigated? must you not have investigated? must they not have investigated?
V-ing perfect
must I not have been investigating? must you not have been investigating? must she not have been investigating? must we not have been investigating? must you not have been investigating? must they not have been investigating?