could dull
Regular verb: dull - dulled- dulled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could dull
you could dull
he could dull
we could dull
you could dull
they could dull 	I could be dulling
you could be dulling
he could be dulling
we could be dulling
you could be dulling
they could be dulling	I could have dulled
you could have dulled
he could have dulled
we could have dulled
you could have dulled
they could have dulled	I could have been dulling
you could have been dulling
he could have been dulling
we could have been dulling
you could have been dulling
they could have been dulling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not dull
you could not dull
he could not dull
we could not dull
you could not dull
they could not dull 	I could not be dulling
you could not be dulling
he could not be dulling
we could not be dulling
you could not be dulling
they could not be dulling	I could not have dulled
you could not have dulled
he could not have dulled
we could not have dulled
you could not have dulled
they could not have dulled	I could not have been dulling
you could not have been dulling
he could not have been dulling
we could not have been dulling
you could not have been dulling
they could not have been dulling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I dull?
could you dull?
could he dull?
could we dull?
could you dull?
could they dull? 	could I be dulling?
could you be dulling?
could he be dulling?
could we be dulling?
could you be dulling?
could they be dulling? 	could I have dulled?
could you have dulled?
could he have dulled?
could we have dulled?
could you have dulled?
could they have dulled? 	could I have been dulling?
could you have been dulling?
could he have been dulling?
could we have been dulling?
could you have been dulling?
could they have been dulling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not dull?
could you not dull?
could he not dull?
could we not dull?
could you not dull?
could they not dull? 	could I not be dulling?
could you not be dulling?
could he not be dulling?
could we not be dulling?
could you not be dulling?
could they not be dulling? 	could I not have dulled?
could you not have dulled?
could he not have dulled?
could we not have dulled?
could you not have dulled?
could they not have dulled? 	could I not have been dulling?
could you not have been dulling?
could he not have been dulling?
could we not have been dulling?
could you not have been dulling?
could they not have been dulling?