English verb conjugation
MUST OCCUR

Regular verb: occur - occurred - occurred

Affirmation

Simple form	V-ing form
I must occur you must occur he must occur we must occur you must occur they must occur	I must be occurring you must be occurring he must be occurring we must be occurring you must be occurring they must be occurring
Perfect	V-ing perfect
I must have occurred you must have occurred he must have occurred we must have occurred you must have occurred they must have occurred	I must have been occurring you must have been occurring he must have been occurring we must have been occurring you must have been occurring they must have been occurring

Negation

Simple form	V-ing form
I must not occur you must not occur he must not occur we must not occur you must not occur they must not occur	I must not be occurring you must not be occurring he must not be occurring we must not be occurring you must not be occurring they must not be occurring
Perfect	V-ing perfect
I must not have occurred you must not have occurred he must not have occurred we must not have occurred you must not have occurred they must not have occurred	I must not have been occurring you must not have been occurring he must not have been occurring we must not have been occurring you must not have been occurring they must not have been occurring

Interrogative form

Simple form	V-ing form
must I occur? must you occur? must he occur? must we occur? must you occur? must they occur?	must I be occurring? must you be occurring? must he be occurring? must we be occurring? must you be occurring? must they be occurring?
Perfect	V-ing perfect
must I have occurred? must you have occurred? must he have occurred? must we have occurred? must you have occurred? must they have occurred?	must I have been occurring? must you have been occurring? must he have been occurring? must we have been occurring? must you have been occurring? must they have been occurring?

Interro-negative form

Simple form	V-ing form
must I not occur? must you not occur? must he not occur? must we not occur? must you not occur? must they not occur?	must I not be occurring? must you not be occurring? must he not be occurring? must we not be occurring? must you not be occurring? must they not be occurring?
Perfect	V-ing perfect
must I not have occurred? must you not have occurred? must he not have occurred? must we not have occurred? must you not have occurred? must they not have occurred?	must I not have been occurring? must you not have been occurring? must he not have been occurring? must we not have been occurring? must you not have been occurring? must they not have been occurring?