I must research you must research he must research we must research you must research they must research
V-ing form
I must be researching you must be researching he must be researching we must be researching you must be researching they must be researching
Perfect
I must have researched you must have researched he must have researched we must have researched you must have researched they must have researched
V-ing perfect
I must have been researching you must have been researching he must have been researching we must have been researching you must have been researching they must have been researching
Negation
Simple form
I must not research you must not research he must not research we must not research you must not research they must not research
V-ing form
I must not be researching you must not be researching he must not be researching we must not be researching you must not be researching they must not be researching
Perfect
I must not have researched you must not have researched he must not have researched we must not have researched you must not have researched they must not have researched
V-ing perfect
I must not have been researching you must not have been researching he must not have been researching we must not have been researching you must not have been researching they must not have been researching
Interrogative form
Simple form
must I research? must you research? must he research? must we research? must you research? must they research?
V-ing form
must I be researching? must you be researching? must he be researching? must we be researching? must you be researching? must they be researching?
Perfect
must I have researched? must you have researched? must he have researched? must we have researched? must you have researched? must they have researched?
V-ing perfect
must I have been researching? must you have been researching? must he have been researching? must we have been researching? must you have been researching? must they have been researching?
Interro-negative form
Simple form
must I not research? must you not research? must he not research? must we not research? must you not research? must they not research?
V-ing form
must I not be researching? must you not be researching? must he not be researching? must we not be researching? must you not be researching? must they not be researching?
Perfect
must I not have researched? must you not have researched? must he not have researched? must we not have researched? must you not have researched? must they not have researched?
V-ing perfect
must I not have been researching? must you not have been researching? must he not have been researching? must we not have been researching? must you not have been researching? must they not have been researching?