could stem
Regular verb: stem - stemmed- stemmed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could stem
you could stem
he could stem
we could stem
you could stem
they could stem 	I could be stemming
you could be stemming
he could be stemming
we could be stemming
you could be stemming
they could be stemming	I could have stemmed
you could have stemmed
he could have stemmed
we could have stemmed
you could have stemmed
they could have stemmed	I could have been stemming
you could have been stemming
he could have been stemming
we could have been stemming
you could have been stemming
they could have been stemming	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't stem
you couldn't stem
he couldn't stem
we couldn't stem
you couldn't stem
they couldn't stem 	I couldn't be stemming
you couldn't be stemming
he couldn't be stemming
we couldn't be stemming
you couldn't be stemming
they couldn't be stemming	I couldn't have stemmed
you couldn't have stemmed
he couldn't have stemmed
we couldn't have stemmed
you couldn't have stemmed
they couldn't have stemmed	I couldn't have been stemming
you couldn't have been stemming
he couldn't have been stemming
we couldn't have been stemming
you couldn't have been stemming
they couldn't have been stemming	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I stem?
could you stem?
could he stem?
could we stem?
could you stem?
could they stem? 	could I be stemming?
could you be stemming?
could he be stemming?
could we be stemming?
could you be stemming?
could they be stemming? 	could I have stemmed?
could you have stemmed?
could he have stemmed?
could we have stemmed?
could you have stemmed?
could they have stemmed? 	could I have been stemming?
could you have been stemming?
could he have been stemming?
could we have been stemming?
could you have been stemming?
could they have been stemming? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I stem?
couldn't you stem?
couldn't he stem?
couldn't we stem?
couldn't you stem?
couldn't they stem? 	couldn't I be stemming?
couldn't you be stemming?
couldn't he be stemming?
couldn't we be stemming?
couldn't you be stemming?
couldn't they be stemming? 	couldn't I have stemmed?
couldn't you have stemmed?
couldn't he have stemmed?
couldn't we have stemmed?
couldn't you have stemmed?
couldn't they have stemmed? 	couldn't I have been stemming?
couldn't you have been stemming?
couldn't he have been stemming?
couldn't we have been stemming?
couldn't you have been stemming?
couldn't they have been stemming?