could dull
Regular verb: dull - dulled- dulled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could dull
you could dull
she could dull
we could dull
you could dull
they could dull 	I could be dulling
you could be dulling
she could be dulling
we could be dulling
you could be dulling
they could be dulling	I could have dulled
you could have dulled
she 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
she 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 couldn't dull
you couldn't dull
she couldn't dull
we couldn't dull
you couldn't dull
they couldn't dull 	I couldn't be dulling
you couldn't be dulling
she couldn't be dulling
we couldn't be dulling
you couldn't be dulling
they couldn't be dulling	I couldn't have dulled
you couldn't have dulled
she couldn't have dulled
we couldn't have dulled
you couldn't have dulled
they couldn't have dulled	I couldn't have been dulling
you couldn't have been dulling
she couldn't have been dulling
we couldn't have been dulling
you couldn't have been dulling
they couldn't have been dulling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I dull?
could you dull?
could she dull?
could we dull?
could you dull?
could they dull? 	could I be dulling?
could you be dulling?
could she be dulling?
could we be dulling?
could you be dulling?
could they be dulling? 	could I have dulled?
could you have dulled?
could she 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 she 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 	
couldn't I dull?
couldn't you dull?
couldn't she dull?
couldn't we dull?
couldn't you dull?
couldn't they dull? 	couldn't I be dulling?
couldn't you be dulling?
couldn't she be dulling?
couldn't we be dulling?
couldn't you be dulling?
couldn't they be dulling? 	couldn't I have dulled?
couldn't you have dulled?
couldn't she have dulled?
couldn't we have dulled?
couldn't you have dulled?
couldn't they have dulled? 	couldn't I have been dulling?
couldn't you have been dulling?
couldn't she have been dulling?
couldn't we have been dulling?
couldn't you have been dulling?
couldn't they have been dulling?