English verb conjugation
MUST OCCUR

Regular verb: occur - occurred - occurred

Affirmation

Simple form	V-ing form
I must occur you must occur she must occur we must occur you must occur they must occur	I must be occurring you must be occurring she 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 she 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 she 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 mustn't occur you mustn't occur she mustn't occur we mustn't occur you mustn't occur they mustn't occur	I mustn't be occurring you mustn't be occurring she mustn't be occurring we mustn't be occurring you mustn't be occurring they mustn't be occurring
Perfect	V-ing perfect
I mustn't have occurred you mustn't have occurred she mustn't have occurred we mustn't have occurred you mustn't have occurred they mustn't have occurred	I mustn't have been occurring you mustn't have been occurring she mustn't have been occurring we mustn't have been occurring you mustn't have been occurring they mustn't have been occurring

Interrogative form

Simple form	V-ing form
must I occur? must you occur? must she occur? must we occur? must you occur? must they occur?	must I be occurring? must you be occurring? must she 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 she 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 she 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
mustn't I occur? mustn't you occur? mustn't she occur? mustn't we occur? mustn't you occur? mustn't they occur?	mustn't I be occurring? mustn't you be occurring? mustn't she be occurring? mustn't we be occurring? mustn't you be occurring? mustn't they be occurring?
Perfect	V-ing perfect
mustn't I have occurred? mustn't you have occurred? mustn't she have occurred? mustn't we have occurred? mustn't you have occurred? mustn't they have occurred?	mustn't I have been occurring? mustn't you have been occurring? mustn't she have been occurring? mustn't we have been occurring? mustn't you have been occurring? mustn't they have been occurring?