English verb conjugation
MUST UNDERPIN

Regular verb: underpin - underpinned - underpinned

Affirmation

Simple form	V-ing form
I must underpin you must underpin he must underpin we must underpin you must underpin they must underpin	I must be underpinning you must be underpinning he must be underpinning we must be underpinning you must be underpinning they must be underpinning
Perfect	V-ing perfect
I must have underpinned you must have underpinned he must have underpinned we must have underpinned you must have underpinned they must have underpinned	I must have been underpinning you must have been underpinning he must have been underpinning we must have been underpinning you must have been underpinning they must have been underpinning

Negation

Simple form	V-ing form
I must not underpin you must not underpin he must not underpin we must not underpin you must not underpin they must not underpin	I must not be underpinning you must not be underpinning he must not be underpinning we must not be underpinning you must not be underpinning they must not be underpinning
Perfect	V-ing perfect
I must not have underpinned you must not have underpinned he must not have underpinned we must not have underpinned you must not have underpinned they must not have underpinned	I must not have been underpinning you must not have been underpinning he must not have been underpinning we must not have been underpinning you must not have been underpinning they must not have been underpinning

Interrogative form

Simple form	V-ing form
must I underpin? must you underpin? must he underpin? must we underpin? must you underpin? must they underpin?	must I be underpinning? must you be underpinning? must he be underpinning? must we be underpinning? must you be underpinning? must they be underpinning?
Perfect	V-ing perfect
must I have underpinned? must you have underpinned? must he have underpinned? must we have underpinned? must you have underpinned? must they have underpinned?	must I have been underpinning? must you have been underpinning? must he have been underpinning? must we have been underpinning? must you have been underpinning? must they have been underpinning?

Interro-negative form

Simple form	V-ing form
must I not underpin? must you not underpin? must he not underpin? must we not underpin? must you not underpin? must they not underpin?	must I not be underpinning? must you not be underpinning? must he not be underpinning? must we not be underpinning? must you not be underpinning? must they not be underpinning?
Perfect	V-ing perfect
must I not have underpinned? must you not have underpinned? must he not have underpinned? must we not have underpinned? must you not have underpinned? must they not have underpinned?	must I not have been underpinning? must you not have been underpinning? must he not have been underpinning? must we not have been underpinning? must you not have been underpinning? must they not have been underpinning?