I must preascertain you must preascertain he must preascertain we must preascertain you must preascertain they must preascertain
V-ing form
I must be preascertaining you must be preascertaining he must be preascertaining we must be preascertaining you must be preascertaining they must be preascertaining
Perfect
I must have preascertained you must have preascertained he must have preascertained we must have preascertained you must have preascertained they must have preascertained
V-ing perfect
I must have been preascertaining you must have been preascertaining he must have been preascertaining we must have been preascertaining you must have been preascertaining they must have been preascertaining
Negation
Simple form
I must not preascertain you must not preascertain he must not preascertain we must not preascertain you must not preascertain they must not preascertain
V-ing form
I must not be preascertaining you must not be preascertaining he must not be preascertaining we must not be preascertaining you must not be preascertaining they must not be preascertaining
Perfect
I must not have preascertained you must not have preascertained he must not have preascertained we must not have preascertained you must not have preascertained they must not have preascertained
V-ing perfect
I must not have been preascertaining you must not have been preascertaining he must not have been preascertaining we must not have been preascertaining you must not have been preascertaining they must not have been preascertaining
Interrogative form
Simple form
must I preascertain? must you preascertain? must he preascertain? must we preascertain? must you preascertain? must they preascertain?
V-ing form
must I be preascertaining? must you be preascertaining? must he be preascertaining? must we be preascertaining? must you be preascertaining? must they be preascertaining?
Perfect
must I have preascertained? must you have preascertained? must he have preascertained? must we have preascertained? must you have preascertained? must they have preascertained?
V-ing perfect
must I have been preascertaining? must you have been preascertaining? must he have been preascertaining? must we have been preascertaining? must you have been preascertaining? must they have been preascertaining?
Interro-negative form
Simple form
must I not preascertain? must you not preascertain? must he not preascertain? must we not preascertain? must you not preascertain? must they not preascertain?
V-ing form
must I not be preascertaining? must you not be preascertaining? must he not be preascertaining? must we not be preascertaining? must you not be preascertaining? must they not be preascertaining?
Perfect
must I not have preascertained? must you not have preascertained? must he not have preascertained? must we not have preascertained? must you not have preascertained? must they not have preascertained?
V-ing perfect
must I not have been preascertaining? must you not have been preascertaining? must he not have been preascertaining? must we not have been preascertaining? must you not have been preascertaining? must they not have been preascertaining?