English verb conjugation
MUST SPIFF

Regular verb: spiff - spiffed - spiffed

Affirmation

Simple form	V-ing form
I must spiff you must spiff he must spiff we must spiff you must spiff they must spiff	I must be spiffing you must be spiffing he must be spiffing we must be spiffing you must be spiffing they must be spiffing
Perfect	V-ing perfect
I must have spiffed you must have spiffed he must have spiffed we must have spiffed you must have spiffed they must have spiffed	I must have been spiffing you must have been spiffing he must have been spiffing we must have been spiffing you must have been spiffing they must have been spiffing

Negation

Simple form	V-ing form
I must not spiff you must not spiff he must not spiff we must not spiff you must not spiff they must not spiff	I must not be spiffing you must not be spiffing he must not be spiffing we must not be spiffing you must not be spiffing they must not be spiffing
Perfect	V-ing perfect
I must not have spiffed you must not have spiffed he must not have spiffed we must not have spiffed you must not have spiffed they must not have spiffed	I must not have been spiffing you must not have been spiffing he must not have been spiffing we must not have been spiffing you must not have been spiffing they must not have been spiffing

Interrogative form

Simple form	V-ing form
must I spiff? must you spiff? must he spiff? must we spiff? must you spiff? must they spiff?	must I be spiffing? must you be spiffing? must he be spiffing? must we be spiffing? must you be spiffing? must they be spiffing?
Perfect	V-ing perfect
must I have spiffed? must you have spiffed? must he have spiffed? must we have spiffed? must you have spiffed? must they have spiffed?	must I have been spiffing? must you have been spiffing? must he have been spiffing? must we have been spiffing? must you have been spiffing? must they have been spiffing?

Interro-negative form

Simple form	V-ing form
must I not spiff? must you not spiff? must he not spiff? must we not spiff? must you not spiff? must they not spiff?	must I not be spiffing? must you not be spiffing? must he not be spiffing? must we not be spiffing? must you not be spiffing? must they not be spiffing?
Perfect	V-ing perfect
must I not have spiffed? must you not have spiffed? must he not have spiffed? must we not have spiffed? must you not have spiffed? must they not have spiffed?	must I not have been spiffing? must you not have been spiffing? must he not have been spiffing? must we not have been spiffing? must you not have been spiffing? must they not have been spiffing?