I could dull you could dull she could dull we could dull you could dull they could dull
V-ing form
I could be dulling you could be dulling she could be dulling we could be dulling you could be dulling they could be dulling
Perfect
I could have dulled you could have dulled she could have dulled we could have dulled you could have dulled they could have dulled
V-ing perfect
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
I could not dull you could not dull she could not dull we could not dull you could not dull they could not dull
V-ing form
I could not be dulling you could not be dulling she could not be dulling we could not be dulling you could not be dulling they could not be dulling
Perfect
I could not have dulled you could not have dulled she could not have dulled we could not have dulled you could not have dulled they could not have dulled
V-ing perfect
I could not have been dulling you could not have been dulling she 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
could I dull? could you dull? could she dull? could we dull? could you dull? could they dull?
V-ing form
could I be dulling? could you be dulling? could she be dulling? could we be dulling? could you be dulling? could they be dulling?
Perfect
could I have dulled? could you have dulled? could she have dulled? could we have dulled? could you have dulled? could they have dulled?
V-ing perfect
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
could I not dull? could you not dull? could she not dull? could we not dull? could you not dull? could they not dull?
V-ing form
could I not be dulling? could you not be dulling? could she not be dulling? could we not be dulling? could you not be dulling? could they not be dulling?
Perfect
could I not have dulled? could you not have dulled? could she not have dulled? could we not have dulled? could you not have dulled? could they not have dulled?
V-ing perfect
could I not have been dulling? could you not have been dulling? could she not have been dulling? could we not have been dulling? could you not have been dulling? could they not have been dulling?